Your body has a kind of built-in thermostat that it can regulate. When you get a fever, the first thing that happens is that the thermostat gets cranked up a few notches when the body decides it needs to be hotter e.g. to kill off an infection more effectively. The body then suddenly finds itself at an actual core temperature lower than the “set” temperature of the thermostat. This produces the feeling of cold forcing you to get under a blanket, drink hot beverages etc. in order to raise your core temperature to the “set” temperature as fast as possible. So that feeling is the way your body communicates to you what it needs to be done right now. You also get involuntary shivers which are a way of raising core temperature as well (rapid muscle movement spends their stored energy and releases heat).
This is the most accurate answer. Some talk about relative temperatures, and you body does notice relative temperature differences (going from ice water to tap feels warmer than it should, etc.), but the reason you have chills as your fever begins is the thermostat set point going up before your body’s temp even changes at all. Then, when the fever breaks and your thermostat goes down, you feel hot and get sweaty.
Your thermostat set point changes depending on the level of inflammation the infection is causing. There are too numerous to count factors that can contribute to this, but they include infectious organism load, the amount of recently destroyed infectious organisms, your daily cortisol levels, your immune function and the many factors that affect that, etc.
To add on, your medicine also tells your body’s thermostat to go back down, so then you feel hot. It’s also why when a fever breaks you end up having this Hoss Cartwright moment where you sweat profusely.
It should be in series rather than simultaneous. your memory of high fevers can be a little touchy, especially if you have it at night and it’s mixed with fever dreams
And when the fever “breaks” the thermostat gets turned back down to normal, and you feel hot and start to sweat profusely as an attempt to get rid of the excess heat.
You feel weak/tired as this is going on because your body is expending additional resources to rid it of the pathogen that is causing illness to begin with. Illness throws our equilibrium off and our bodies respond by going into low power mode until we return to normal.
If anyone here has ever cooked their own chicken stock and made chicken broth you’ll know that that water is dense with healthy stuff and it seems to take longer to heat up than normal water. When that warm liquid goes into your belly it can really help heat your body up along with all the healthy stuff to help your body. That’s why chicken noods is the best remedy when you’re sick imo.
Most people aren't making their own stock though, most just use packaged or canned chicken noodle. But salt is good when you're sick, mostly why they recommend soups or broths.
Yep, I noticed exactly this several years ago and tested it multiple times and it's true. To add a minor thing: you feel cold only while your fever is getting higher, once the temp is reached, your back to normal. You also get hot and sweaty when you take a paracetamol or ibuprofen as they reduce the fever.
Last year when I had COVID I passed out from overheating myself.
I had a relatively mild fever ~100-102, however I couldn't shake the cold feeling out of my bones. I covered up in tons of blankets, sitting at my computer. Before I knew it suddenly went from freezing cold to REALLY HOT. I stood up to deshell the blankets off of me, and take my sweat pants off. On the way up I blacked out for the first time in my life and threw an elbow through the wall.
TLDR : shorts and one blanket ONLY when you have a fever
So is it recommended to actually get under a blanket and eat hot soup, or it would just make the fever worse and it’s better to brave the cold feeling?
Blanket and soup. The fever is actually helpful in fighting infection, up to a point. So you don't want to take medications to lower the fever either. But you should keep an eye on your temperature and consult a doctor if it's higher than ____. I'm not going to give a number since I have no medical training.
Fevers over 108 degrees can cause brain damage. You body will almost never give you a fever that high, it usually only happens when the ambient air is that hot, like in a closed car in the sun. Even temperatures up to 105 and 106 degrees are safe, but that doesnt mean they are comfortable and medication is recommended if the fever is making you uncomfortable.
When I was reading up on this same topic a while back, I started wondering about taking fever meds as well. I figured that if the fever is actually a helpful bodily response, then fever meds ought to extend the length of a sickness, right? What I read was that there is data to support that, however if what we're REALLY interested in is "how long will I feel bad", then fever meds help alleviate that (and other symptoms) to make the sickness more tolerable, and it ends up kinda being a wash from a somewhat more subjective point of view. Either your sickness is slightly shorter, but you feel worse, or your sickness is slightly longer and you feel less bad.
Basically, it seemed the advice was to just take meds if you feel like you need them.
That makes sense. I think I would rather just be fully sick for a couple days and be better sooner, but I can see how others might have a different preference.
My mum used to give us fever meds and used ice cold water or even a bath to cool us down. She says 39-40 degree celcsius is the line between "cold water" and ER.
Never died before yet so it must work but i keep seeing people recommend opposite of cold.
One thing I found out is that your body has no idea how hot or cold the body is. Is just knows the base level set in the hypothalamus is either higher or lower than what the core is sending.
S'why you see naked people who have frozen to death. Their core at some point drops so low in temperature the body suddenly thinks it's boiling hot, will start sweating, and the person has the instinctual need to strip to "cool off" hastening their death.
I'm not familiar with stories of this happening absent some sort of drug / illness / disorder. You're saying that hypothermia can result in paradoxical sweating, by itself?
> Twenty to fifty percent of hypothermia deaths are associated with paradoxical undressing.
https://en.m.wikipedia.org/wiki/Hypothermia#:~:text=Twenty%20to%20fifty%20percent%20of,the%20rate%20of%20heat%20loss.
Paradoxical undressing. Fits with the body not knowing its temperature, but knowing its off by an extreme degree.
Similar to how your body's not good at telling the difference between scalding water or ice cold water. The sensation just completely overwhelms your nerves so the only signal to your brain receives is pain, immense pain.
It's crude but the effect is the same ; getting away from that stimulus.
So in summary, you don't actually feel cold *because* you have a fever, instead you have a fever *because* you feel cold! You brain tricks you into thinking you're cold so that you'll try to warm up, and that increases your body temperature and gives you the fever.
As for part 2, "why do we feel so weak and tired when sick/have a fever?": Your body works best in a very narrow temperature range. However, most pathogens (bacteria and viruses that make you sick) work in an *even narrower* temperature range. So when your immune system detects an infection, it turns up your temperature to give it an edge in fighting off the pathogen. That's why you feel like crap - your body is way too hot to function optimally, but at least it's functioning better than whatever is hurting you.
>As for part 2, "why do we feel so weak and tired when sick/have a fever?": Your body works best in a very narrow temperature range. However, most pathogens (bacteria and viruses that make you sick) work in an *even narrower* temperature range. So when your immune system detects an infection, it turns up your temperature to give it an edge in fighting off the pathogen. That's why you feel like crap - your body is way too hot to function optimally, but at least it's functioning better than whatever is hurting you.
also, your body is fighting a war against the infection. it needs resources to do so, such as your energy which makes you feel tired.
> you don't actually feel cold because you have a fever, instead you have a fever because you feel cold!
this sounds a bit confusing because I personally associate 'high temperature' and 'feeling cold' as both being caused by having 'a fever'. the fever causes you to feel cold, which leads to a raise in body temperature.
if you 'have a fever because you feel cold', then what is the term for the phenomenon that is causing you to feel cold? is there one?
I see what you mean. Dictionary.com gives these as the first 2 definitions for "fever":
1. an abnormal condition of the body, characterized by undue rise in temperature, quickening of the pulse, and disturbance of various body functions.
2. an abnormally high body temperature.
You're using the first definition, while I'm using the second one.
I suppose, speaking precisely, an "increased hypothalamic set point" is what causes you to feel cold, which in turn causes "pyrexia" or elevated body temperature.
> That's why you feel like crap - your body is way too hot to function optimally, but at least it's functioning better than whatever is hurting you.
Your immune system fights better in higher temperatures as well, the high temp hurts the pathogen and boosts your own system
Honestly, that's kinda cool. When I got covid a few months ago, I spent an entire day FREEZING. I had a heater on, I had a bunch of showers that were so hot it was absurd (and almost hurt) then curled up under a blanket. But it was all because my body was CERTAIN that I wasn't warm enough, because it redefined what "warm enough" was.
I can confirm this firsthand. I developed a rare flavor of penicillin allergy and apart from mind shattering pain, the other side effect was an inability to regulate body temp. I was swinging back and forth between Danger Fever and nothing a few times a day. When it was fever time I was blankets blankets blankets fireplace you name it nothing was warm enough, and then I'd be sweating like a sex worker in church.
Fever cranks up and you're friggin freezing Mr bigglesworth.
I dont get it, then why does the thermometer already records a higher temperature when you have already had the chills? There is no pending time to get to “newly set temperature from said thermostat”.
So, when I have a fever and I feel cold, is it right to warm myself up (maybe with extra blankets)? Or is that wrong because I already have a fever and I am already too warm?
Well that too, but it’s kinda minor really. The increase in temperature during fever isn’t that large when compared to the range of ambient temperatures that we find more or less comfortable.
It might be that, say, you are still under a blanket when the fever levels off and the body no longer needs to be raising its temperature. Or otherwise the fever is already breaking and the body has started to lower its temperature.
Those involuntary shivers are called "rigors" and it's the best way to raise the temperature. When I had sepsis, the doctor (bless him) gave me some Demerol to stop the rigors. I had never felt so calm, sure, and nimble as when I was under the Demerol. No wonder it's addictive.
Once you learn that this is normal, you can embrace it. Your body is sending you the first signals of being infected? Get hot! Burn that motherfucker away!
Yup. This is correct.
I see it all the time with one of my kiddos. She wakes up screaming and shivering saying she’s cold and her temp by the thermometer is normal. Then I take it 10min later and it’s 103. Takes her little body a bit to warm up to the new set point but she feels it first.
Imagine if the body did something like this if you became obese.
Body says: "nope, turning off the hunger hormones. You and I both know we don't need anymore food right now."
\> Edit 1: With that why do we feel so weak and tired when sick/have a fever
To answer this since people already answered the main part of the question. When your body is sick, it's trying to kill off an invasion of foreign bodies that are very much determined to live even at your expanse. This process consumes a large part of your energy, thus leaving less energy for the rest of your bodily functions, thus making you tired.
Ofc that's not the only parameter at play but as far as I'm aware it's the main one :)
It's weird to think that something internally consumes enough energy to even have an effect on you. How something you can't see or really even feel is enough to pull you out of the threshold of "enough energy" to lift something heavy.
Want your mind blown even more? Processing the brain signals required for thought requires an enormous amount of energy, to the point that your brain uses a *lot* more of your energy than any other organ in your body! I don’t remember the exact number but something like 20% of your body’s energy budget is needed just for running your brain.
That makes a lot of sense actually. I'd imagine there's probably some correlation between people who are stressed/depressed and their sleeping habits (totally not projecting lol) because of that. Very interesting
Not a noticeable amount, the brain is processing every sensory input, conscious and unconscious thought and regulating a ton of processes so doing math is not a significant increase.
Not many, as the processing power is spread across a lot of different brain processes. But you might notice an easier time focusing on math problems if you eat some food first to give yourself energy!
That's not the full picture. Voluntary muscle function under strain is heavily regulated by dopamine uptake. The result is, that without dopamine, you can't command your full strength. Even if you physically could, your body will refuse without dopamine.
Part of the sensation of misery comes from elevated cortisol and lowered dopamine levels. Your muscles by and large can operate at maximum capacity almost instantly for exactly the purpose of lifting something heavy in a theoretical emergency.
Actually depleting the muscle glycogen reserves only occurs during very prolonged illness, malnutrition, or repeated exhaustion.
The sensation of being weak and depleted has more to do with the body trying to convince you to take it easy than it does any genuine physical inability. You will recover faster if you wait to do intense things till after you're sick so your body puts the kaibash on excessive energy spending even if you have the calories to spare.
Your brain consumes a whopping 20% of your total energy throughout the day. If youve ever had something that mentally drained you even though you were just sitting there like taking a test.
Other bodily systems specifically are ramped down in order to have the immune system fight at its maximum
You aren’t hungry when you’re sick because your body doesn’t want to waste resources on digesting and breaking down food when those resources are needed elsewhere
*You* are warmer, therefore the world around you is *colder* than you. And your body doesn't want to lose that heat, so cold becomes unpleasant and your body does things like shivering to generate more heat, even when there's no danger of you getting too cold.
Edit: as more people have pointed out, this isn't entirely accurate. Heat transfer is more important than relative temperature. However, how fast heat transfers depends in part on said relative temperatures.
Yes. Here, experiment that's fun:
Get a small bowl of hot (but not burning) water, a small bowl of cold water, and a larger bowl of room-temperature water.
Stick one hand in the hot water and one hand in the cold. Wait like 30-60 seconds for your skin's temperature to change.
Then put both hands into the bowl of room-temp water. What do you feel?
>Paradoxical undressing?
Which is often followed by terminal burrowing. The lizard part of our brain is initiating some kind of last ditch ancient burrowing instinct to try to keep warm. The paradoxical undressing is because as your body's thermoregulatory systems fail blood that was being kept from your extremities to maintain core temperature is suddenly released and you get a hot flash throughout your body and people will begin to undress because they feel overwhelmingly warm. Once this happens death is not usually far behind.
This is really interesting for an unrelated reason.
The temp in my house is relatively constant, however, most nights after I eat dinner, I find myself feeling cold…so I load up on blankets & socks & hoodies. And then every night at like 2 am I wake up DYING OF HEAT STROKE. I bet this is when the blood that was stolen from my extremities to aid in digestion in my core is no longer needed and is released back to my extremities.
Unless I’m totally wrong…but this would make sense.
Huh, guess I almost died when I was younger walking home through a blizzard after my car got stuck. My hands and legs got warm suddenly before they went numb but I didn't have the urge to dig a hole
Wait, how does that work? The outside temperature is what is cooling your body, but for it to feel hotter it needs to be warmer than your body, and if its warmer it couldn't have cooled you that far down. A sudden increase in temperature in the ambient temperature?
Basically, when you are suffering from hypothermia your body constricts blood vessels in your limbs to keep your core warm and to stop losing heat through limbs that aren’t vital. You start to shiver, generating heat. Shivering takes a lot of energy for your body to do. After a certain point, your body isn’t able to maintain the energy needed to keep shivering, so in response the blood vessels in your limbs dilate again. You now feel hot due to the blood rushing back everywhere. A lot of people will feel *too* hot and start to take off clothes, resulting in a quicker death
I don't know that it's fully understood, but the theory I once read said that the body effectively starts to give up on keeping the core warm. Since it was originally trying to accomplish this by reducing circulation throughout the body, the body relaxes and all that warm blood suddenly starts flooding your extremities. This sudden rush of warm blood to areas that were cold earlier causes a sudden temperature shift that starts to make people feel like they're overheating.
Huh.
Several years ago, I was doing the trail on the jungfraujoch with my wife. It was pretty cold, of course, with snow everywhere, but it wasn't freezing - we didn't need to wear gloves, for example.
I had done the trail to the hut 10 years ago, and enjoyed it alot. This year was different though - we were maybe 1/3 of the way through, and I started experiencing what I assume was altitude sickness. I was pretty tired, and if I moved too quickly/suddenly, I felt a bit gross for about 30 seconds or so. The path towards the hut is a slight uphill and I was also having struggles trying to get up some of the steeper parts (just due to slipping).
It didn't take too long before I just started feeling really WARM. I hike a fair bit, so I started slowly unzipping/undressing as it progressed. I remember thinking how odd it was to be so warm in such a situation, but I had assumed it was just because of how hard I was working in some sections.
Now, I'm not so sure. I don't recall actually checking to see if I was sweating or not before taking anything off (my instinct was to unzip first so I never had wet/sweaty clothes).
I did eventually get to the hut. They served food there, so I lay down, got some food, recharged, and got back with no issues.
iirc your body spends a lot of energy trying to keep your internal organs warm and let's your extremities freeze. Once your body starts lacking the energy to do so, the blood rushes back out to the extremities. It causes the person to feel a sudden rush of heat and and feel like they're burning up. With the heat amd being delirious/hypothermic they strip off their clothes to cool down.
I also remember reading that its still not 100% understood.
There's actually documented phenomena where people in extreme cases of hypothermia are compelled to undress because they feel too hot. Its called [Paradoxical Undressing](https://en.m.wikipedia.org/wiki/Hypothermia#Paradoxical_undressing)
The statistics look pretty high to be considered isolated incidents. You tend to be compelled to do weird things under stress
Heat transfer can have some intuitively weird outcomes.
For example, if you have drinks cooling in a cooler, they will cool down faster if the ice is melting because to melt the ice you need to heat the ice and the heat comes from the cans.
Also, when a lake freezes, the lake is heating air around it.
> For example, if you have drinks cooling in a cooler, they will cool down faster if the ice is melting because to melt the ice you need to heat the ice and the heat comes from the cans.
what you mean isn't wrong, but i disagree with how you are saying it.
We can treat a cooler of ice and canned drinks as effectively a closed system (scale of things we care about). The drinks and ice are going to be trying to equalize their temperatures because warmer stuff is going to try to warm up the colder stuff.
What you are getting at is that there is extra energy needed for the phase change from ice to water, so while 31 F to 32 F might only take 1 BTU and while 32 F to 33 F might only take 1 BTU, the change of ice to water is going to take a bunch of energy as well, so 32 F ice to 32 F water is going to cool the drinks down in addition.
And adding salt to the mix lowers the freezing point of water below 32 F. This means that you can have water touching the ice and the cans which is going to transfer the heat from the cans to the ice far better than air would, which helps the cans cool down faster.
NOTE:
1 BTU is not the energy to move an unknown volume of water 1 degree fahrenheit, but you get the idea.
Note 2...
I know that you know this, but it made my brain happy to clarify this for me. And for others that might not follow what you mean later.
That's a little bit different, it has more to do with the fact that the latent heat of the phase transition (basically the extra energy it takes to melt something in this case) is significantly larger than the energy difference in ice of different temperatures.
Usually when a person with hypothermia suddenly feels warm is because the body is sort of "giving up" Your body will lower circulation to extremities to keep your core warm. When it hits a certain point of too cold the body relaxes and releases all that warn blood from your core providing a flush of warmth, which is what causes people to undress, parts that were very cold, like your hands and tip of the nose are suddenly on fire.
Reports from hypothermia victims who lived say that near the end, you feel warm and sleepy.
Incidentally, that’s why people used to give people alcohol in the olden days when they were freezing—the alcohol lowers your body temp slightly, so you FEEL warmer. It wasn’t actually that great an idea, though.
Even though both hands are in the same temperature water at the end, the hand that was soaked in hot water will feel the water being colder than then hand soaked in cold water.
Your body only feels heat transfer.
This is why if you stick a piece of wood and metal in the freezer and then grab them an hour later, the metal feels colder even though they are at the same temperature.
You feel the metal as colder because it conducts heat away from you faster.
Blew my mind when someone on Reddit explained it with taking clothes out of the dryer. That comfortably warm pair of socks and the scalding hot metal button on your jeans are *the same temperature*! One just happens to transfer heat much more easily than the other.
Still wrinkles my brain (but not my clothes!)
That's why if you have fabric oven mitts you need to make FUCKING SURE they never get wet.
Nothing like 3rd degree steam burns on your dominant hand to ruin your cupcakes.
Ughhhhh this is true, I remember learning this the hard way as well and doing my nice cast iron crockpot. Worst part is I had to get the pot off the linoleum so I had to just pull my hand back to the dry part and get it hoisted before I could tend to the hand
Silicone coated mitts are amazing for preventing this
Also important to point out:
Feeling *heat transfer* as opposed to absolute temperature is a feature, not bug.
You can walk around in chilly winter air for quite awhile without losing critical body heat, as air transfers heat away from you slowly.
But you cannot survive for long submersed in the same temperature of water, as it transfers heat away from you quickly.
it's more like heat flow: that's why it feels cold to get into a pool when it's the same temperature as the air you're already standing in. the water readily conducts heat away from your body and it has an enormous capacity to hold heat.
Not even that. Your skin perceives the TRANSFER of heat to or from. Heat leaving your body is perceived as cold, heat entering your body is perceived as warm.
Metal conducts heat better than paper. Take a metal plate and a book, both at room temp. If you put one hand on a metal plate and one hand on a book. Even though they are both the same temperature, the metal will feel colder because it conducts heat away from your hand faster than the book.
If you find a material that is the same temperature as your skin, you feel nothing, other than the tactile touch of the object.
EDIT: Interesting side note. The gel they coat stunt men/women in when they light them on fire, absorbs heat so well, that some of the time the stunt worker is actually shivering despite being on fire and wearing 4 layers of clothes.
I wanted to share this with another person who understands(and potentially enjoys) heat transfer: the hair on your head is a fantastic insulator, until it needs to become a conductor.
The tiny strands of individual hair work together as a great insulator to keep your brain warm. Until it’s time to become a conductor.
When your brain gets too hot, you start leaking water from your skin. This causes the strands of hair to clump together and they start to group and they become fairly closely similar in size to the fins on the heat sink of your graphics card. So they went from being tiny strands trapping air, to thicker strands that approximate the size of the fins in your card’s heat sink. But they are still made of hair which doesn’t conduct heat very well. Well, Jesus had an answer for that when he designed us in his lab: water.
The thick-and-clumped-together strands of hair now have water in them, and each gram of water that evaporates takes 2,250joules of latent heat energy with it. So now we have a heat sink that removes heat better than the best heat sinks the computer industry could make, because the computer heat sinks don’t have water leaking out of them to evaporate.
tl;dr- the hair on your head is an excellent insulator until it needs to be an excellent conductor.
Thanks for reading.
Thanks!
Stoned hippyengineer absolutely loved going to heat transfer class and imagining all this crazy shit. Then I realized I was understanding the material on a level deeper than I ever could have hoped if I went to class sober.
Perfect 5/7 would recommend going to heat transfer class stoned
Awesome! I wish I took more biomechanics classes while I was getting my Mech E degree. This is a sweet example of how fascinating the human body is when looking at it through an engineering lens!
Body feels heat *transfer*, not actual temp. You don’t feel the temperature of an ice cube touching you finger, you feel the transfer of heat from your finger to the ice cube.
If you made you fingers super cold, and then touched the ice cube, you wouldn’t notice the sensation of the ice cube as much as you would if you just stepped out of a hot tub and touched the ice cube.
-Engineer who fucking *loves* heat transfer.
In addition to the other comments, it's also why ''wind chill'' is a thing.
Wind doesn't make things colder, but it takes heat away from your body faster, making it feel as if it was colder.
If it's -5c temp outside, with a wind chill of -15c, you will feel the same heat transfer as if it was -15c with no wind.
Furthermore if you put out a solution with a freezing point of -10c, it will not freeze, it will simply get to -5c quicker than if there was no wind.
Back when I lived in Minnesota, I had maybe a half-mile hike from the office to the bus stop. I was bundled up nicely, so I wasn’t in any danger, but damn, that was a long cold walk, usually into the wind.
One day I get to the bus stop, step inside the little shelter out of the wind, and am instantly roasting. Pulling off my scarf and hat, opening my wool coat, going “Whew! My god, how hot is it?” There was a bank across the way with a big sign with a digital readout of time and temp. I look up, and it’s zero degrees F. Because wind chill heat transfer is a Big Damn Deal.
Man yeah, like taking a shower when it's fairly cold in the house. First stick your hand in and you're like "oh shit, is this too hot" then several seconds you're like "no no, it's fine, it's not that hot."
I know you got 50 replies with examples and are probably not reading them anymore but my favourite one is this:
Next time you get out of the shower and the tiles are so cold that you quickly step on the warm towel appreciate that both the tiles and the towel actually have the same (room) temperature.
The tiles are just better at transferring the shower heat out of your feet.
Yes, the people doing research on this won a Nobel Prize for research on how temperature and touch are interpreted by the body.
https://www.nobelprize.org/uploads/2021/10/advanced-medicine-2021.pdf
You're used to a certain levall of heat loss that makes you feel normal.
If you're experiencing more heat loss, eg because your fever makes you warmer, or you have burned skin that makes it easier to lose heat, or you're wet and there's some breeze, you feel cooler even if everything else is the same.
Our regular body processes do a good job of keeping us at that temperature. So our body doesn’t need to do anything special to generate more heat if the outside temperature is regular.
to build on this - the reason why evolution has selected for this apparently paradoxical behaviour is because it confers a selective advantage.
Specifically, fever is an attempt to generate extra heat and 'cook' the pathogens out of your body, since those pathogens have inferior heat compensation cytochemistry compared to the rest of you. Your body can cope with being overheated by a bit, but microbes die off quite quickly. Your body is trying to run hot to kill the invaders.
So if you 'felt hot' and then tried to cool yourself... You would cool down back to baseline and wouldn't actually kill the pathogen. Your body is trying to make you feel cold so that you wrap up and get even warmer so that you can kill the infection.
This is part of a theory that a colleague of mine was working on. You should consider it an unproven hypothesis, because I can't be arsed looking out the primary resources to cite here.
That's just plain false.
It's not the temperature difference between you and the outside world, it is the temperature difference between your body and what your body wants to be at.
When getting sick, your body *wants* to get to a higher temperature (fever), so it does all the things that your body can do to raise temperature. Goosebumps and shivers and comfort when putting on something warm, which are things you normally associate with being cold.
And from my personal experience, once your body gets to its desired fever temperature, the chills stop and then you definitely do feel very hot.
This is a poor and misconstrued way to describe this mechanism. Not sure how this is top comment. It has to do with relativity to your internal “thermostat” set by the hypothalamus. This explains why when you work out and your temperature increases, you feel hot since your internal thermostat is still set at normal physiologic temperature - unlike a fever where it is set higher and you begin to feel cold, even if your temperature initially begins at normal temperatures.
That can't be right. Or bodies are very much designed to lose heat when they're to warm. Sweating for example. When you're too hot and you're sweating you're body definitely "wants" to lose that heat.
The body has a goal to keep the temp at around 37.5C. If it is too cold it either needs to take in energy from its surroundings, generate that energy through metabolising fat, shivering etc.
If it is too warm it will shed that heat through evaporation of sweat.
So if your body is too hot (aka a fever) it will definitely "want" to lose that heat. Hyperthermia is as deadly as hypothermia and a body working properly in a safe environmental temp will maintain your body temp accordingly.
So the point is not your body now is warmer in comparison to the temperature, but what is the mechanism that gives the perception of cold when you are warm.
The reason you feel cold is because the body's internal set point has been raised to try and fight off the infection (virus or bacteria).
The way your body does this is by incorporating the mechanisms you associate with being cold e.g. Shivering.
So you have it kind of backwards. It's not that you are warm and the air is now relatively colder. It's that your body wants to be warmer and to get there it makes your body do things that you associate with being cold (because your body wants to be warm in those situations too).
Your body has an internal thermostat, kinda like a house thermostat.
If you were to suddenly turn your house thermostat up from 20 C to 25 C, the house would suddenly go “oh no, I’m colder than I should be. I need to warm up so I can reach 25 C.” And it pumps heat into the house.
That’s the same reason you feel cold when you have a fever. Your body is telling you you need to be at 38 C instead of 36 C, and it triggers the feeling of being colder than you should be. That prompts you to seek out heat to help warm you up.
The extra heat can help kill pathogens, but your body also struggles and breaks down if it’s too hot.
I'll have to strongly disagree with the heat transfer hypthesis described in multiple posts here. The sensation of cold/heat during fever is internal sensation usually caused by a mismatch between internal thermostat temperature and real body temperature. Whereas the things you describe come from an sensation form your environment (outside sensation which can be influenced by many factors).
Your body has a thermostat which regulates temperature usually it is set around 98,6 F. During normal situation everyting is in balance, you lose as much heat as you produce and you feel neither really warm or cold.
During fever your body decides to set temperature to 100 F (to kill bacteria and viruses more effectively). Even if you are already warm (lets say 99F) your body temperature does not match the desired thermostat (internal sensation of cold) and does everything to get to that set temperature (shiver, extera layers of clothing) to increase heat production/conservation resulting in higher body temperature (fever). Going outside into 50 F you would almost certainly feel even more cold (outside sentation cold).
Conversely during an extended Sauna session the core temperature of a healthy person could also be raised to 99F. Because the thermostat is still set to its normal temperature at 98,6 the body feels it has too much heat (internal sensation of warm). Now it tries everything to cool you down (mainly sweating). If you would go outside into mild winter cold (around 50F) you could still sense outside as cool though percieving your internal as too warm. In this case the outside temperature is not nearly as unpleasent because it helps your body to bring it to the desired temperature.
Heat transfer would be roughly the same in both situations (outside sensation of cold), Internal heat sensation in both situaions can vary drastically bases on internal set temperature.
> I'll have to strongly disagree with the heat transfer hypthesis described in multiple posts here
And rightly so, because it is wrong.
The feeling of being cold comes from the actual body temperature being lower than the "desired" body temperature.
During a fever your "desired" temperature is elevated. The body "wants" to be warmer. Which in turn means that your current temperature is suddenly "too cold". Our bodies aren't actually capable of measuring "energy transfer" in the manner suggested.
Anecdote: One time I was biking home in a torrential downpour on a rather chilly early fall night. By the time I got home I was soaked to the bone. After changing into dry clothes I poured myself a glass of water from the room temperature jug and it tasted warm?!?
Is it possible that someone or something heated up my water? Sure. But more realistically it's the fact that my body temperature was way lower than normal that caused it to taste warm to me.
Fever chills are the same concept, but the other way around.
I remember being outside in the winter with shitty boots for hours. I got to the point where I couldn't feel my feet (not good), I got home and ran a bath of cold water and stuck my foot in there.
It felt like I lit it on fire.
Haha yes, I remember when i would shovel the snow in my driveway, then I got the great idea of running my hands under hot water to warm them up, it felt like i was melting the flesh off my hands
Our bodies don't actually feel temperature -- we feel energy flowing into, or out of, our bodies.
Energy flow is dependent on a lot of things, like material properties -- this is why metal feels colder than wood, even though they're the same temperature (it's more conductive so it pulls energy out of you faster.)
When you have a fever there's a bigger temperature difference between you and the air -- which means more energy is leaving your body. Also you might be sweating -- and sweating makes energy leave your body faster as well
Your immune system works better at higher temperatures.
Your body wants a higher temperature.
Its your bodies way of telling you to pile on more blankets.
With more blankets your temperature goes up, and or you can maintain the current temperature with fewer calories.
Your immune system doesn’t “work better” at high temperatures, it’s really the opposite. Everything works less well at higher temps including the ability of a virus to continue replicating. Your body is sacrificing its own capabilities in order to slow down and kill the virus by the very same mechanism that reduces your bodies own functioning.
Humans are the best animal at getting rid of heat, all we need to do is take off our clothes, animals with fur can't do that. When you have a fever, that's your body trying to make itself so hot that whatever is attacking you can't survive. As you get a fever, if you felt hot, you would take steps to get cooler, like throwing off your blankets, or taking your shirt off. This would stop the fever, which isn't what your body wants. By making you feel cold, you stay in bed with the blanket on you, making the fever more effective at doing its job.
What we feel isn't the absolute temperature of things, we feel the rate at which heat is conducted. For example, at the beach, even if the water and air are at the same temperature, the water will always feel colder because it takes heat away from you quicker.
When you have a fever your body temperature is higher than usual, so you transfer heat to the surroundings faster. Therefore you feel colder.
If youre outside in below freezing weather, have a nice jacket/sweater etc but no gloves, even just for a few minutes outside. Then go in, turn on the cold tapwater and run it over your hand - it will feel warm, but if you run your wrist that was warm and covered its cold. Same thing in reverse, you are hot and the air around you feels cold rather than your hand being cold and the cool water feeling warm.
You don't feel temperature. You can only feel heat transfer: you can feel losing heat and gaining heat. For example, when a breeze blows, or you stand in front of a fan, you feel cooler, but the temperature hasn't actually changed! Rather, your body releases some heat and that heat stays close to your skin; when a wind blows away that warmer air near your skin, your body loses more heat to the air to recreate that layer. This is also how jackets and blankets work; they trap in the warm air your body heats up. And it's also why metal tends to feel very hot or very cold. It isn't hotter or colder than the environment, but metal transmits heat very, very well, so the heat transfer happens quickly, which is why you feel it so much.
Note that these processes aren't *active* processes. Your body doesn't *release* heat as some sort of activity. It's just two items of different temperatures coming to thermal equilibrium, except that your body produces its own heat all the time to replace the lost heat.
When you have a fever, you are warmer, so you lose more heat to the air around you, and therefore you feel colder. If your fever is 101°F, your 69°F room feels like it's 67°, which is a little on the cold side.
There are multiple different mechanisms at play here, because... the body is COMPLEX! lol. I'm gunna break it down physiologically
1) - An infection is caused by a pathogen (bacteria, virus, fungi, etc..) This pathogen is recognized by the immune system as foreign. Immune cells then are triggered, which causes a release of chemicals from those cells that will cause a physiological response (these chemicals can be cytokines, Interleukins, Interferons, etc..).
2) Some of these chemicals (specifically Interleukin- 1, Interleukin - 6, Interleukin -8, Interferon- Gamma) flow through your body and reach your brain.
3) Your body temperature is regulated by a "thermostat" in the brain ( specifically the hypothalamus, of which temperature regulation is just one of the functions). The chemicals released into the body due to infection will go to the hypothalamus and tell it to "raise the temp, we got bugs causing some shit somewhere. Cook em up". This causes a rise in body temperature from its normal resting temp to a higher one, which we call a fever.
4) Along with this, we have a function of the human body to regulate how our blood vessels work. Blood vessels can constrict and can expand depending on how much blood is needed in a particular organ. Blood carries white blood cells, red blood cells, basically everything you need to live and fight off disease, and it is *warm (*and blood cools itself when it flows through the skin to allow heat to dissipate). In certain conditions, such as eating, blood vessels supplying the skin will constrict in order to ensure more blood is sent to the gut to provide energy for digestion of food. In an infection, blood vessels keep more blood around the "vital" organs (heart, brain, lungs, etc) because these organs are a necessity for the body to function. This further increases core body temperature.
5) So now you have blood concentrated in the core organs internally and chemicals causing your thermostat to raise the temperature. The difference between the temperature between the internal organs and outermost organs (skin) is greater. This difference is what causes the feeling of "cold" as sensory receptors on and around the skin and other outer organs send signals to the brain via a spinal cord nerve tract called the "spinothalamic tract" that the difference between the environment and internal temperatures is greater. Think about when you go from inside your house in winter versus in summer. In winter, the outside temperature is lower than your internal temperature, thus you feel "cold". Where as in summer, the outside temperature can be greater than the inner temperature, so you feel hot.
This difference is what is the cause of shivering. Shivering is one of the body's mechanisms to raise it's temperature via muscle activity. As muscles work they use energy from glycogen and other substances derived from the food we eat. This energy usage is not 100% efficient, and the un-used energy is given off as heat (Newton's law of thermodynamics). This is the body's way of attempting to heat the outer organs, as the skeletal musculature is closely attached to the skin via the subcutaneous tissue and fascia and shivering lets heat to flow out to the outer portion. Think about it. When was the last time you felt cold and then felt your liver or spleen or pancreas shaking inside you trying to stay warm? they don't.
6) Weakness and tiredness are also related to these mechanisms. When those chemicals (cytokines, Interleukins, interferons) are released, some of them cause weakness and tiredness as well. This has a very good purpose: when fighting an infection, the body wants you to use all your resources to overcome this infection as fast as possible. Weakness is there to ensure you do not do something dumb, like a boxing match or run a marathon, while fighting the infection. Body doesnt want to share resources for unnecessary activities. Tiredness is to promote sleep. During sleep, your body releases more chemicals (complement system, etc) to fight infection. basically your immune system is MORE active while you are asleep than when you're awake. Basically the body wants you to be in bed and asleep so it doesn't have to divert energy towards frivolous junk activities while it is busy slaughtering foreign pathogens.
You don't feel temperature itself so much as you feel change in temperature.
You feel cold in cold weather because the air is constantly sucking your body heat out of your relatively hot body. In weather around 75 F° or so (I don't remember the actual temperature), the heat you're losing is the same as the heat you're generating, so you barely feel temperature at all.
When you have a fever, however, your body is much hotter. This means you have more heat to dump into the surrounding air, so you'll feel colder than you normally would in the same air.
There is a great experiment that you can do at home:
Prepare 3 bowls of water, one cold, one natural temp and one (kind of) hot.
Put your left hand on the cold and your right on the hoy one and leave it there for a while.
Then put both on the natural temperature one. For one hand it will feel cold, for the other hot.
Your body has a kind of built-in thermostat that it can regulate. When you get a fever, the first thing that happens is that the thermostat gets cranked up a few notches when the body decides it needs to be hotter e.g. to kill off an infection more effectively. The body then suddenly finds itself at an actual core temperature lower than the “set” temperature of the thermostat. This produces the feeling of cold forcing you to get under a blanket, drink hot beverages etc. in order to raise your core temperature to the “set” temperature as fast as possible. So that feeling is the way your body communicates to you what it needs to be done right now. You also get involuntary shivers which are a way of raising core temperature as well (rapid muscle movement spends their stored energy and releases heat).
This is the most accurate answer. Some talk about relative temperatures, and you body does notice relative temperature differences (going from ice water to tap feels warmer than it should, etc.), but the reason you have chills as your fever begins is the thermostat set point going up before your body’s temp even changes at all. Then, when the fever breaks and your thermostat goes down, you feel hot and get sweaty.
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Your thermostat set point changes depending on the level of inflammation the infection is causing. There are too numerous to count factors that can contribute to this, but they include infectious organism load, the amount of recently destroyed infectious organisms, your daily cortisol levels, your immune function and the many factors that affect that, etc.
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To add on, your medicine also tells your body’s thermostat to go back down, so then you feel hot. It’s also why when a fever breaks you end up having this Hoss Cartwright moment where you sweat profusely.
This is so helpful, I too swing back and forth between overheated and freezing, and I have adhd which has a huge effect on cortisol levels.
What about when you feel like you're boiling hot and freezing cold at the same time?
It should be in series rather than simultaneous. your memory of high fevers can be a little touchy, especially if you have it at night and it’s mixed with fever dreams
Thanks, /u/AssPelt_McFuzzyButt
And when the fever “breaks” the thermostat gets turned back down to normal, and you feel hot and start to sweat profusely as an attempt to get rid of the excess heat. You feel weak/tired as this is going on because your body is expending additional resources to rid it of the pathogen that is causing illness to begin with. Illness throws our equilibrium off and our bodies respond by going into low power mode until we return to normal.
You'll also feel weak and tired because the enzymes in your muscles don't work well at those higher temps.
Ohhhhh
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I seem to remember reading that testosterone blunts the immune response. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5075254/
This is the answer. Exact analogy that my A&P text uses.
Why would you need to know this to work at a [grocery store](https://en.wikipedia.org/wiki/A%26P)
Lmao Anatomy and Physiology. Forgot that was also the name of a grocery store
LOL, I figured by your username that you used to work at store 1095.
\^ This guy reddits.
I ain’t smart enough to know if this is “true” but I do know it’s very well said.
Can confirm that it is true.
This guy is smart enough!
You're pretty smart to recognize that the previous commenter was smart
i like turtles
If anyone here has ever cooked their own chicken stock and made chicken broth you’ll know that that water is dense with healthy stuff and it seems to take longer to heat up than normal water. When that warm liquid goes into your belly it can really help heat your body up along with all the healthy stuff to help your body. That’s why chicken noods is the best remedy when you’re sick imo.
chicken nudes, you say?
Some of the best noods you can get. Especially if it’s from someone you love.
Well that....and all the sodium in it.
I make homemade stock and you don’t need much salt at all if you have plenty of herbs and such. But store bought stuff has tons of salt!
Most people aren't making their own stock though, most just use packaged or canned chicken noodle. But salt is good when you're sick, mostly why they recommend soups or broths.
Yep, I noticed exactly this several years ago and tested it multiple times and it's true. To add a minor thing: you feel cold only while your fever is getting higher, once the temp is reached, your back to normal. You also get hot and sweaty when you take a paracetamol or ibuprofen as they reduce the fever.
Last year when I had COVID I passed out from overheating myself. I had a relatively mild fever ~100-102, however I couldn't shake the cold feeling out of my bones. I covered up in tons of blankets, sitting at my computer. Before I knew it suddenly went from freezing cold to REALLY HOT. I stood up to deshell the blankets off of me, and take my sweat pants off. On the way up I blacked out for the first time in my life and threw an elbow through the wall. TLDR : shorts and one blanket ONLY when you have a fever
Classic 'overshoot' controls situation.
zeta << 1 eh? God I did not enjoy systems classes.
I miss that stuff sometimes. I'm an EE that moved into middle/upper management in Manufacturing and I miss getting to do problems like that.
When I had COVID I spent the worst hours of my fever in the bathtub, alternately adding cold and hot water to regulate my temperature
Fever pro.
So is it recommended to actually get under a blanket and eat hot soup, or it would just make the fever worse and it’s better to brave the cold feeling?
Blanket and soup. The fever is actually helpful in fighting infection, up to a point. So you don't want to take medications to lower the fever either. But you should keep an eye on your temperature and consult a doctor if it's higher than ____. I'm not going to give a number since I have no medical training.
Fevers over 108 degrees can cause brain damage. You body will almost never give you a fever that high, it usually only happens when the ambient air is that hot, like in a closed car in the sun. Even temperatures up to 105 and 106 degrees are safe, but that doesnt mean they are comfortable and medication is recommended if the fever is making you uncomfortable.
When I was reading up on this same topic a while back, I started wondering about taking fever meds as well. I figured that if the fever is actually a helpful bodily response, then fever meds ought to extend the length of a sickness, right? What I read was that there is data to support that, however if what we're REALLY interested in is "how long will I feel bad", then fever meds help alleviate that (and other symptoms) to make the sickness more tolerable, and it ends up kinda being a wash from a somewhat more subjective point of view. Either your sickness is slightly shorter, but you feel worse, or your sickness is slightly longer and you feel less bad. Basically, it seemed the advice was to just take meds if you feel like you need them.
That makes sense. I think I would rather just be fully sick for a couple days and be better sooner, but I can see how others might have a different preference.
I believe in the US, we say 104°. Once it hits 105, seek medical attention to avoid long-term damage.
My mum used to give us fever meds and used ice cold water or even a bath to cool us down. She says 39-40 degree celcsius is the line between "cold water" and ER. Never died before yet so it must work but i keep seeing people recommend opposite of cold.
One thing I found out is that your body has no idea how hot or cold the body is. Is just knows the base level set in the hypothalamus is either higher or lower than what the core is sending. S'why you see naked people who have frozen to death. Their core at some point drops so low in temperature the body suddenly thinks it's boiling hot, will start sweating, and the person has the instinctual need to strip to "cool off" hastening their death.
I'm not familiar with stories of this happening absent some sort of drug / illness / disorder. You're saying that hypothermia can result in paradoxical sweating, by itself?
> Twenty to fifty percent of hypothermia deaths are associated with paradoxical undressing. https://en.m.wikipedia.org/wiki/Hypothermia#:~:text=Twenty%20to%20fifty%20percent%20of,the%20rate%20of%20heat%20loss.
.... eep
Paradoxical undressing. Fits with the body not knowing its temperature, but knowing its off by an extreme degree. Similar to how your body's not good at telling the difference between scalding water or ice cold water. The sensation just completely overwhelms your nerves so the only signal to your brain receives is pain, immense pain. It's crude but the effect is the same ; getting away from that stimulus.
Is this also why I’m often cold during pregnancy even though there’s more blood flow/volume than usual?
I always heard the opposite for pregnancy. My wife was basically a space heater when she was pregnant.
Whenever I get sick, I climb under my electric blanket and turn it up. Best way I have found to not get that cold shaky feeling when sick.
So in summary, you don't actually feel cold *because* you have a fever, instead you have a fever *because* you feel cold! You brain tricks you into thinking you're cold so that you'll try to warm up, and that increases your body temperature and gives you the fever. As for part 2, "why do we feel so weak and tired when sick/have a fever?": Your body works best in a very narrow temperature range. However, most pathogens (bacteria and viruses that make you sick) work in an *even narrower* temperature range. So when your immune system detects an infection, it turns up your temperature to give it an edge in fighting off the pathogen. That's why you feel like crap - your body is way too hot to function optimally, but at least it's functioning better than whatever is hurting you.
>As for part 2, "why do we feel so weak and tired when sick/have a fever?": Your body works best in a very narrow temperature range. However, most pathogens (bacteria and viruses that make you sick) work in an *even narrower* temperature range. So when your immune system detects an infection, it turns up your temperature to give it an edge in fighting off the pathogen. That's why you feel like crap - your body is way too hot to function optimally, but at least it's functioning better than whatever is hurting you. also, your body is fighting a war against the infection. it needs resources to do so, such as your energy which makes you feel tired.
> you don't actually feel cold because you have a fever, instead you have a fever because you feel cold! this sounds a bit confusing because I personally associate 'high temperature' and 'feeling cold' as both being caused by having 'a fever'. the fever causes you to feel cold, which leads to a raise in body temperature. if you 'have a fever because you feel cold', then what is the term for the phenomenon that is causing you to feel cold? is there one?
I see what you mean. Dictionary.com gives these as the first 2 definitions for "fever": 1. an abnormal condition of the body, characterized by undue rise in temperature, quickening of the pulse, and disturbance of various body functions. 2. an abnormally high body temperature. You're using the first definition, while I'm using the second one. I suppose, speaking precisely, an "increased hypothalamic set point" is what causes you to feel cold, which in turn causes "pyrexia" or elevated body temperature.
> That's why you feel like crap - your body is way too hot to function optimally, but at least it's functioning better than whatever is hurting you. Your immune system fights better in higher temperatures as well, the high temp hurts the pathogen and boosts your own system
This is one of those things that's almost always wrong in movies and TV shows. Mostly they show the person feeling hot when getting a fever.
Honestly, that's kinda cool. When I got covid a few months ago, I spent an entire day FREEZING. I had a heater on, I had a bunch of showers that were so hot it was absurd (and almost hurt) then curled up under a blanket. But it was all because my body was CERTAIN that I wasn't warm enough, because it redefined what "warm enough" was.
I can confirm this firsthand. I developed a rare flavor of penicillin allergy and apart from mind shattering pain, the other side effect was an inability to regulate body temp. I was swinging back and forth between Danger Fever and nothing a few times a day. When it was fever time I was blankets blankets blankets fireplace you name it nothing was warm enough, and then I'd be sweating like a sex worker in church. Fever cranks up and you're friggin freezing Mr bigglesworth.
I dont get it, then why does the thermometer already records a higher temperature when you have already had the chills? There is no pending time to get to “newly set temperature from said thermostat”.
So, when I have a fever and I feel cold, is it right to warm myself up (maybe with extra blankets)? Or is that wrong because I already have a fever and I am already too warm?
So takings meds kill the fever, it actually slows down the process of killing the infection?
So should you wrap up when shivering from fever, or try to stay cool?
Interesting. I had assumed it was because out body gets hot thus everything feels cold. It's cool to know it's kind of the opposite.
Well that too, but it’s kinda minor really. The increase in temperature during fever isn’t that large when compared to the range of ambient temperatures that we find more or less comfortable.
If your body wants to get hot then why do you still sweat heavily when feverish. Seems like that part of the body doesn't get the message?
It might be that, say, you are still under a blanket when the fever levels off and the body no longer needs to be raising its temperature. Or otherwise the fever is already breaking and the body has started to lower its temperature.
Those involuntary shivers are called "rigors" and it's the best way to raise the temperature. When I had sepsis, the doctor (bless him) gave me some Demerol to stop the rigors. I had never felt so calm, sure, and nimble as when I was under the Demerol. No wonder it's addictive.
Thanks!
Once you learn that this is normal, you can embrace it. Your body is sending you the first signals of being infected? Get hot! Burn that motherfucker away!
ELI5 - the old saying feed a cold, starve a fever
Yup. This is correct. I see it all the time with one of my kiddos. She wakes up screaming and shivering saying she’s cold and her temp by the thermometer is normal. Then I take it 10min later and it’s 103. Takes her little body a bit to warm up to the new set point but she feels it first.
Thermal homeostasis in action when fighting with a pathogen.
I appreciate your efforts for telling us
Imagine if the body did something like this if you became obese. Body says: "nope, turning off the hunger hormones. You and I both know we don't need anymore food right now."
I found out I had appendicitis when I was shivering in a full hot shower. Body is amazing at telling you something is wrong.
\> Edit 1: With that why do we feel so weak and tired when sick/have a fever To answer this since people already answered the main part of the question. When your body is sick, it's trying to kill off an invasion of foreign bodies that are very much determined to live even at your expanse. This process consumes a large part of your energy, thus leaving less energy for the rest of your bodily functions, thus making you tired. Ofc that's not the only parameter at play but as far as I'm aware it's the main one :)
It's weird to think that something internally consumes enough energy to even have an effect on you. How something you can't see or really even feel is enough to pull you out of the threshold of "enough energy" to lift something heavy.
Yeah the body is weird in the sense that it's simultaneously terrifyingly fragile and incredibly resilient
Want your mind blown even more? Processing the brain signals required for thought requires an enormous amount of energy, to the point that your brain uses a *lot* more of your energy than any other organ in your body! I don’t remember the exact number but something like 20% of your body’s energy budget is needed just for running your brain.
That makes a lot of sense actually. I'd imagine there's probably some correlation between people who are stressed/depressed and their sleeping habits (totally not projecting lol) because of that. Very interesting
Can I burn calories doing math problems?
Not a noticeable amount, the brain is processing every sensory input, conscious and unconscious thought and regulating a ton of processes so doing math is not a significant increase.
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An alternate reality where nerds bully jocks
There's an episode of Sliders.
Not many, as the processing power is spread across a lot of different brain processes. But you might notice an easier time focusing on math problems if you eat some food first to give yourself energy!
That's not the full picture. Voluntary muscle function under strain is heavily regulated by dopamine uptake. The result is, that without dopamine, you can't command your full strength. Even if you physically could, your body will refuse without dopamine. Part of the sensation of misery comes from elevated cortisol and lowered dopamine levels. Your muscles by and large can operate at maximum capacity almost instantly for exactly the purpose of lifting something heavy in a theoretical emergency. Actually depleting the muscle glycogen reserves only occurs during very prolonged illness, malnutrition, or repeated exhaustion. The sensation of being weak and depleted has more to do with the body trying to convince you to take it easy than it does any genuine physical inability. You will recover faster if you wait to do intense things till after you're sick so your body puts the kaibash on excessive energy spending even if you have the calories to spare.
If you wake up, literally don't move all day, then go to bed you will burn about 1700 calories.
Your brain consumes a whopping 20% of your total energy throughout the day. If youve ever had something that mentally drained you even though you were just sitting there like taking a test.
Other bodily systems specifically are ramped down in order to have the immune system fight at its maximum You aren’t hungry when you’re sick because your body doesn’t want to waste resources on digesting and breaking down food when those resources are needed elsewhere
*You* are warmer, therefore the world around you is *colder* than you. And your body doesn't want to lose that heat, so cold becomes unpleasant and your body does things like shivering to generate more heat, even when there's no danger of you getting too cold. Edit: as more people have pointed out, this isn't entirely accurate. Heat transfer is more important than relative temperature. However, how fast heat transfers depends in part on said relative temperatures.
Does this mean the body doesnt actually feel heat, just heat relative to itself?
Yes. Here, experiment that's fun: Get a small bowl of hot (but not burning) water, a small bowl of cold water, and a larger bowl of room-temperature water. Stick one hand in the hot water and one hand in the cold. Wait like 30-60 seconds for your skin's temperature to change. Then put both hands into the bowl of room-temp water. What do you feel?
So in a state of Hypothermia, the person feels warmer?
Exactly. If a person suffering from hypothermia suddenly says they feel warm, that’s a bad sign.
Except that’s a completely different effect than what’s happening with the bowls of water.
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Paradoxical undressing?
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This has honestly been one of the most interesting comment chains I've read in a while
>Paradoxical undressing? Which is often followed by terminal burrowing. The lizard part of our brain is initiating some kind of last ditch ancient burrowing instinct to try to keep warm. The paradoxical undressing is because as your body's thermoregulatory systems fail blood that was being kept from your extremities to maintain core temperature is suddenly released and you get a hot flash throughout your body and people will begin to undress because they feel overwhelmingly warm. Once this happens death is not usually far behind.
“ terminal burrowing” also sometimes called “hide and die” syndrome
This is really interesting for an unrelated reason. The temp in my house is relatively constant, however, most nights after I eat dinner, I find myself feeling cold…so I load up on blankets & socks & hoodies. And then every night at like 2 am I wake up DYING OF HEAT STROKE. I bet this is when the blood that was stolen from my extremities to aid in digestion in my core is no longer needed and is released back to my extremities. Unless I’m totally wrong…but this would make sense.
And yes I have hypothyroidism as well as generally poor circulation
Huh, guess I almost died when I was younger walking home through a blizzard after my car got stuck. My hands and legs got warm suddenly before they went numb but I didn't have the urge to dig a hole
I think when that burrowing instinct kicks in you’re not really conscious of your actions and likely delirious and acting on instinct alone.
If you change your jeans, are they still the same?
Only if they were made by Theseus.
Ah yes, I remember my college philosophy class and the classic *Jorts of Theseus* thought experiment.
Like free your mind and your ass will follow?
I don't think that's how it goes, but I like it.
I LEARNED THIS FROM ARCHER!!!!
Upvoting cause I learned something and archer was mentioned where I also saw this
Wait, how does that work? The outside temperature is what is cooling your body, but for it to feel hotter it needs to be warmer than your body, and if its warmer it couldn't have cooled you that far down. A sudden increase in temperature in the ambient temperature?
Basically, when you are suffering from hypothermia your body constricts blood vessels in your limbs to keep your core warm and to stop losing heat through limbs that aren’t vital. You start to shiver, generating heat. Shivering takes a lot of energy for your body to do. After a certain point, your body isn’t able to maintain the energy needed to keep shivering, so in response the blood vessels in your limbs dilate again. You now feel hot due to the blood rushing back everywhere. A lot of people will feel *too* hot and start to take off clothes, resulting in a quicker death
I don't know that it's fully understood, but the theory I once read said that the body effectively starts to give up on keeping the core warm. Since it was originally trying to accomplish this by reducing circulation throughout the body, the body relaxes and all that warm blood suddenly starts flooding your extremities. This sudden rush of warm blood to areas that were cold earlier causes a sudden temperature shift that starts to make people feel like they're overheating.
Happens on Everest all the time.
Huh. Several years ago, I was doing the trail on the jungfraujoch with my wife. It was pretty cold, of course, with snow everywhere, but it wasn't freezing - we didn't need to wear gloves, for example. I had done the trail to the hut 10 years ago, and enjoyed it alot. This year was different though - we were maybe 1/3 of the way through, and I started experiencing what I assume was altitude sickness. I was pretty tired, and if I moved too quickly/suddenly, I felt a bit gross for about 30 seconds or so. The path towards the hut is a slight uphill and I was also having struggles trying to get up some of the steeper parts (just due to slipping). It didn't take too long before I just started feeling really WARM. I hike a fair bit, so I started slowly unzipping/undressing as it progressed. I remember thinking how odd it was to be so warm in such a situation, but I had assumed it was just because of how hard I was working in some sections. Now, I'm not so sure. I don't recall actually checking to see if I was sweating or not before taking anything off (my instinct was to unzip first so I never had wet/sweaty clothes). I did eventually get to the hut. They served food there, so I lay down, got some food, recharged, and got back with no issues.
iirc your body spends a lot of energy trying to keep your internal organs warm and let's your extremities freeze. Once your body starts lacking the energy to do so, the blood rushes back out to the extremities. It causes the person to feel a sudden rush of heat and and feel like they're burning up. With the heat amd being delirious/hypothermic they strip off their clothes to cool down. I also remember reading that its still not 100% understood.
There's actually documented phenomena where people in extreme cases of hypothermia are compelled to undress because they feel too hot. Its called [Paradoxical Undressing](https://en.m.wikipedia.org/wiki/Hypothermia#Paradoxical_undressing) The statistics look pretty high to be considered isolated incidents. You tend to be compelled to do weird things under stress
Heat transfer can have some intuitively weird outcomes. For example, if you have drinks cooling in a cooler, they will cool down faster if the ice is melting because to melt the ice you need to heat the ice and the heat comes from the cans. Also, when a lake freezes, the lake is heating air around it.
> For example, if you have drinks cooling in a cooler, they will cool down faster if the ice is melting because to melt the ice you need to heat the ice and the heat comes from the cans. what you mean isn't wrong, but i disagree with how you are saying it. We can treat a cooler of ice and canned drinks as effectively a closed system (scale of things we care about). The drinks and ice are going to be trying to equalize their temperatures because warmer stuff is going to try to warm up the colder stuff. What you are getting at is that there is extra energy needed for the phase change from ice to water, so while 31 F to 32 F might only take 1 BTU and while 32 F to 33 F might only take 1 BTU, the change of ice to water is going to take a bunch of energy as well, so 32 F ice to 32 F water is going to cool the drinks down in addition. And adding salt to the mix lowers the freezing point of water below 32 F. This means that you can have water touching the ice and the cans which is going to transfer the heat from the cans to the ice far better than air would, which helps the cans cool down faster. NOTE: 1 BTU is not the energy to move an unknown volume of water 1 degree fahrenheit, but you get the idea. Note 2... I know that you know this, but it made my brain happy to clarify this for me. And for others that might not follow what you mean later.
Yup that is correct. I deliberately wrote it the way I did to get the brain wrinkles going.
That's a little bit different, it has more to do with the fact that the latent heat of the phase transition (basically the extra energy it takes to melt something in this case) is significantly larger than the energy difference in ice of different temperatures.
Not by a little either. It takes more energy to evaporate a gram of water than it does to bring it from 0 (at liquid state) to boiling.
Usually when a person with hypothermia suddenly feels warm is because the body is sort of "giving up" Your body will lower circulation to extremities to keep your core warm. When it hits a certain point of too cold the body relaxes and releases all that warn blood from your core providing a flush of warmth, which is what causes people to undress, parts that were very cold, like your hands and tip of the nose are suddenly on fire.
Warm and sleepy. That’s the feeling right before you go to sleep in the snow and die
It's actually a pretty common thing to find people who died of hypothermia having taken off all their clothes because at the end they feel so hot.
Reports from hypothermia victims who lived say that near the end, you feel warm and sleepy. Incidentally, that’s why people used to give people alcohol in the olden days when they were freezing—the alcohol lowers your body temp slightly, so you FEEL warmer. It wasn’t actually that great an idea, though.
It also dilates your blood vessels
Wet
Horny.
Shart.
Lonely.
Well this is an OnlyFans I've never seen before.
This is Reddit. We’re expecting you to tell us how to feel.
The hand that was in warm water feels cold, and the hand that was in cold water feels warm
Depressed
No way you leave us hanging like that. Tell us what we’d feel.
Even though both hands are in the same temperature water at the end, the hand that was soaked in hot water will feel the water being colder than then hand soaked in cold water.
Feel confused!
Like peeing my pants
Your body only feels heat transfer. This is why if you stick a piece of wood and metal in the freezer and then grab them an hour later, the metal feels colder even though they are at the same temperature. You feel the metal as colder because it conducts heat away from you faster.
Blew my mind when someone on Reddit explained it with taking clothes out of the dryer. That comfortably warm pair of socks and the scalding hot metal button on your jeans are *the same temperature*! One just happens to transfer heat much more easily than the other. Still wrinkles my brain (but not my clothes!)
That's why if you have fabric oven mitts you need to make FUCKING SURE they never get wet. Nothing like 3rd degree steam burns on your dominant hand to ruin your cupcakes.
This sounds personal
No major injury but a very warm reminder about how heat transfer works.
Ughhhhh this is true, I remember learning this the hard way as well and doing my nice cast iron crockpot. Worst part is I had to get the pot off the linoleum so I had to just pull my hand back to the dry part and get it hoisted before I could tend to the hand Silicone coated mitts are amazing for preventing this
Also important to point out: Feeling *heat transfer* as opposed to absolute temperature is a feature, not bug. You can walk around in chilly winter air for quite awhile without losing critical body heat, as air transfers heat away from you slowly. But you cannot survive for long submersed in the same temperature of water, as it transfers heat away from you quickly.
it's more like heat flow: that's why it feels cold to get into a pool when it's the same temperature as the air you're already standing in. the water readily conducts heat away from your body and it has an enormous capacity to hold heat.
Not even that. Your skin perceives the TRANSFER of heat to or from. Heat leaving your body is perceived as cold, heat entering your body is perceived as warm. Metal conducts heat better than paper. Take a metal plate and a book, both at room temp. If you put one hand on a metal plate and one hand on a book. Even though they are both the same temperature, the metal will feel colder because it conducts heat away from your hand faster than the book. If you find a material that is the same temperature as your skin, you feel nothing, other than the tactile touch of the object. EDIT: Interesting side note. The gel they coat stunt men/women in when they light them on fire, absorbs heat so well, that some of the time the stunt worker is actually shivering despite being on fire and wearing 4 layers of clothes.
I wanted to share this with another person who understands(and potentially enjoys) heat transfer: the hair on your head is a fantastic insulator, until it needs to become a conductor. The tiny strands of individual hair work together as a great insulator to keep your brain warm. Until it’s time to become a conductor. When your brain gets too hot, you start leaking water from your skin. This causes the strands of hair to clump together and they start to group and they become fairly closely similar in size to the fins on the heat sink of your graphics card. So they went from being tiny strands trapping air, to thicker strands that approximate the size of the fins in your card’s heat sink. But they are still made of hair which doesn’t conduct heat very well. Well, Jesus had an answer for that when he designed us in his lab: water. The thick-and-clumped-together strands of hair now have water in them, and each gram of water that evaporates takes 2,250joules of latent heat energy with it. So now we have a heat sink that removes heat better than the best heat sinks the computer industry could make, because the computer heat sinks don’t have water leaking out of them to evaporate. tl;dr- the hair on your head is an excellent insulator until it needs to be an excellent conductor. Thanks for reading.
Wow. That's neat.
Thanks! Stoned hippyengineer absolutely loved going to heat transfer class and imagining all this crazy shit. Then I realized I was understanding the material on a level deeper than I ever could have hoped if I went to class sober. Perfect 5/7 would recommend going to heat transfer class stoned
Awesome! I wish I took more biomechanics classes while I was getting my Mech E degree. This is a sweet example of how fascinating the human body is when looking at it through an engineering lens!
Body feels heat *transfer*, not actual temp. You don’t feel the temperature of an ice cube touching you finger, you feel the transfer of heat from your finger to the ice cube. If you made you fingers super cold, and then touched the ice cube, you wouldn’t notice the sensation of the ice cube as much as you would if you just stepped out of a hot tub and touched the ice cube. -Engineer who fucking *loves* heat transfer.
In addition to the other comments, it's also why ''wind chill'' is a thing. Wind doesn't make things colder, but it takes heat away from your body faster, making it feel as if it was colder. If it's -5c temp outside, with a wind chill of -15c, you will feel the same heat transfer as if it was -15c with no wind. Furthermore if you put out a solution with a freezing point of -10c, it will not freeze, it will simply get to -5c quicker than if there was no wind.
Back when I lived in Minnesota, I had maybe a half-mile hike from the office to the bus stop. I was bundled up nicely, so I wasn’t in any danger, but damn, that was a long cold walk, usually into the wind. One day I get to the bus stop, step inside the little shelter out of the wind, and am instantly roasting. Pulling off my scarf and hat, opening my wool coat, going “Whew! My god, how hot is it?” There was a bank across the way with a big sign with a digital readout of time and temp. I look up, and it’s zero degrees F. Because wind chill heat transfer is a Big Damn Deal.
It's why the water feels like it's boiling if you've been out in the cold all day.
Man yeah, like taking a shower when it's fairly cold in the house. First stick your hand in and you're like "oh shit, is this too hot" then several seconds you're like "no no, it's fine, it's not that hot."
Post hockey I thought my toes would fall off.
I know you got 50 replies with examples and are probably not reading them anymore but my favourite one is this: Next time you get out of the shower and the tiles are so cold that you quickly step on the warm towel appreciate that both the tiles and the towel actually have the same (room) temperature. The tiles are just better at transferring the shower heat out of your feet.
Exactly what I was thinking, that’s freaking incredible!
Yes, the people doing research on this won a Nobel Prize for research on how temperature and touch are interpreted by the body. https://www.nobelprize.org/uploads/2021/10/advanced-medicine-2021.pdf
But if our normal temperature is 98.6F we are already warmer than most environments.... still confused.
You're used to a certain levall of heat loss that makes you feel normal. If you're experiencing more heat loss, eg because your fever makes you warmer, or you have burned skin that makes it easier to lose heat, or you're wet and there's some breeze, you feel cooler even if everything else is the same.
When you have a fever, you are warmer still.
Our regular body processes do a good job of keeping us at that temperature. So our body doesn’t need to do anything special to generate more heat if the outside temperature is regular.
Your skin temperature is cooler than that.
to build on this - the reason why evolution has selected for this apparently paradoxical behaviour is because it confers a selective advantage. Specifically, fever is an attempt to generate extra heat and 'cook' the pathogens out of your body, since those pathogens have inferior heat compensation cytochemistry compared to the rest of you. Your body can cope with being overheated by a bit, but microbes die off quite quickly. Your body is trying to run hot to kill the invaders. So if you 'felt hot' and then tried to cool yourself... You would cool down back to baseline and wouldn't actually kill the pathogen. Your body is trying to make you feel cold so that you wrap up and get even warmer so that you can kill the infection. This is part of a theory that a colleague of mine was working on. You should consider it an unproven hypothesis, because I can't be arsed looking out the primary resources to cite here.
I thought it was because the brain has said "time to increase temp" and you feel cold until the body temp rises.
That's just plain false. It's not the temperature difference between you and the outside world, it is the temperature difference between your body and what your body wants to be at. When getting sick, your body *wants* to get to a higher temperature (fever), so it does all the things that your body can do to raise temperature. Goosebumps and shivers and comfort when putting on something warm, which are things you normally associate with being cold. And from my personal experience, once your body gets to its desired fever temperature, the chills stop and then you definitely do feel very hot.
Sounds ad hoc. You feel hot when you exercise even though the surrounding are colder. Inconsistent logic.
This is a poor and misconstrued way to describe this mechanism. Not sure how this is top comment. It has to do with relativity to your internal “thermostat” set by the hypothalamus. This explains why when you work out and your temperature increases, you feel hot since your internal thermostat is still set at normal physiologic temperature - unlike a fever where it is set higher and you begin to feel cold, even if your temperature initially begins at normal temperatures.
Mods please delete this. This is just inaccurate
That can't be right. Or bodies are very much designed to lose heat when they're to warm. Sweating for example. When you're too hot and you're sweating you're body definitely "wants" to lose that heat. The body has a goal to keep the temp at around 37.5C. If it is too cold it either needs to take in energy from its surroundings, generate that energy through metabolising fat, shivering etc. If it is too warm it will shed that heat through evaporation of sweat. So if your body is too hot (aka a fever) it will definitely "want" to lose that heat. Hyperthermia is as deadly as hypothermia and a body working properly in a safe environmental temp will maintain your body temp accordingly. So the point is not your body now is warmer in comparison to the temperature, but what is the mechanism that gives the perception of cold when you are warm. The reason you feel cold is because the body's internal set point has been raised to try and fight off the infection (virus or bacteria). The way your body does this is by incorporating the mechanisms you associate with being cold e.g. Shivering. So you have it kind of backwards. It's not that you are warm and the air is now relatively colder. It's that your body wants to be warmer and to get there it makes your body do things that you associate with being cold (because your body wants to be warm in those situations too).
Your body has an internal thermostat, kinda like a house thermostat. If you were to suddenly turn your house thermostat up from 20 C to 25 C, the house would suddenly go “oh no, I’m colder than I should be. I need to warm up so I can reach 25 C.” And it pumps heat into the house. That’s the same reason you feel cold when you have a fever. Your body is telling you you need to be at 38 C instead of 36 C, and it triggers the feeling of being colder than you should be. That prompts you to seek out heat to help warm you up. The extra heat can help kill pathogens, but your body also struggles and breaks down if it’s too hot.
I'll have to strongly disagree with the heat transfer hypthesis described in multiple posts here. The sensation of cold/heat during fever is internal sensation usually caused by a mismatch between internal thermostat temperature and real body temperature. Whereas the things you describe come from an sensation form your environment (outside sensation which can be influenced by many factors). Your body has a thermostat which regulates temperature usually it is set around 98,6 F. During normal situation everyting is in balance, you lose as much heat as you produce and you feel neither really warm or cold. During fever your body decides to set temperature to 100 F (to kill bacteria and viruses more effectively). Even if you are already warm (lets say 99F) your body temperature does not match the desired thermostat (internal sensation of cold) and does everything to get to that set temperature (shiver, extera layers of clothing) to increase heat production/conservation resulting in higher body temperature (fever). Going outside into 50 F you would almost certainly feel even more cold (outside sentation cold). Conversely during an extended Sauna session the core temperature of a healthy person could also be raised to 99F. Because the thermostat is still set to its normal temperature at 98,6 the body feels it has too much heat (internal sensation of warm). Now it tries everything to cool you down (mainly sweating). If you would go outside into mild winter cold (around 50F) you could still sense outside as cool though percieving your internal as too warm. In this case the outside temperature is not nearly as unpleasent because it helps your body to bring it to the desired temperature. Heat transfer would be roughly the same in both situations (outside sensation of cold), Internal heat sensation in both situaions can vary drastically bases on internal set temperature.
> I'll have to strongly disagree with the heat transfer hypthesis described in multiple posts here And rightly so, because it is wrong. The feeling of being cold comes from the actual body temperature being lower than the "desired" body temperature. During a fever your "desired" temperature is elevated. The body "wants" to be warmer. Which in turn means that your current temperature is suddenly "too cold". Our bodies aren't actually capable of measuring "energy transfer" in the manner suggested.
You are right, there would be heat transfer sensation but so small that would not explain the chilling feeling
Anecdote: One time I was biking home in a torrential downpour on a rather chilly early fall night. By the time I got home I was soaked to the bone. After changing into dry clothes I poured myself a glass of water from the room temperature jug and it tasted warm?!? Is it possible that someone or something heated up my water? Sure. But more realistically it's the fact that my body temperature was way lower than normal that caused it to taste warm to me. Fever chills are the same concept, but the other way around.
I remember being outside in the winter with shitty boots for hours. I got to the point where I couldn't feel my feet (not good), I got home and ran a bath of cold water and stuck my foot in there. It felt like I lit it on fire.
Haha yes, I remember when i would shovel the snow in my driveway, then I got the great idea of running my hands under hot water to warm them up, it felt like i was melting the flesh off my hands
Our bodies don't actually feel temperature -- we feel energy flowing into, or out of, our bodies. Energy flow is dependent on a lot of things, like material properties -- this is why metal feels colder than wood, even though they're the same temperature (it's more conductive so it pulls energy out of you faster.) When you have a fever there's a bigger temperature difference between you and the air -- which means more energy is leaving your body. Also you might be sweating -- and sweating makes energy leave your body faster as well
I mean energy is heat and vice versa. Laws of thermodynamics basically mean they are a different form of the same thing.
Your immune system works better at higher temperatures. Your body wants a higher temperature. Its your bodies way of telling you to pile on more blankets. With more blankets your temperature goes up, and or you can maintain the current temperature with fewer calories.
Your immune system doesn’t “work better” at high temperatures, it’s really the opposite. Everything works less well at higher temps including the ability of a virus to continue replicating. Your body is sacrificing its own capabilities in order to slow down and kill the virus by the very same mechanism that reduces your bodies own functioning.
Humans are the best animal at getting rid of heat, all we need to do is take off our clothes, animals with fur can't do that. When you have a fever, that's your body trying to make itself so hot that whatever is attacking you can't survive. As you get a fever, if you felt hot, you would take steps to get cooler, like throwing off your blankets, or taking your shirt off. This would stop the fever, which isn't what your body wants. By making you feel cold, you stay in bed with the blanket on you, making the fever more effective at doing its job.
What we feel isn't the absolute temperature of things, we feel the rate at which heat is conducted. For example, at the beach, even if the water and air are at the same temperature, the water will always feel colder because it takes heat away from you quicker. When you have a fever your body temperature is higher than usual, so you transfer heat to the surroundings faster. Therefore you feel colder.
If youre outside in below freezing weather, have a nice jacket/sweater etc but no gloves, even just for a few minutes outside. Then go in, turn on the cold tapwater and run it over your hand - it will feel warm, but if you run your wrist that was warm and covered its cold. Same thing in reverse, you are hot and the air around you feels cold rather than your hand being cold and the cool water feeling warm.
You don't feel temperature. You can only feel heat transfer: you can feel losing heat and gaining heat. For example, when a breeze blows, or you stand in front of a fan, you feel cooler, but the temperature hasn't actually changed! Rather, your body releases some heat and that heat stays close to your skin; when a wind blows away that warmer air near your skin, your body loses more heat to the air to recreate that layer. This is also how jackets and blankets work; they trap in the warm air your body heats up. And it's also why metal tends to feel very hot or very cold. It isn't hotter or colder than the environment, but metal transmits heat very, very well, so the heat transfer happens quickly, which is why you feel it so much. Note that these processes aren't *active* processes. Your body doesn't *release* heat as some sort of activity. It's just two items of different temperatures coming to thermal equilibrium, except that your body produces its own heat all the time to replace the lost heat. When you have a fever, you are warmer, so you lose more heat to the air around you, and therefore you feel colder. If your fever is 101°F, your 69°F room feels like it's 67°, which is a little on the cold side.
There are multiple different mechanisms at play here, because... the body is COMPLEX! lol. I'm gunna break it down physiologically 1) - An infection is caused by a pathogen (bacteria, virus, fungi, etc..) This pathogen is recognized by the immune system as foreign. Immune cells then are triggered, which causes a release of chemicals from those cells that will cause a physiological response (these chemicals can be cytokines, Interleukins, Interferons, etc..). 2) Some of these chemicals (specifically Interleukin- 1, Interleukin - 6, Interleukin -8, Interferon- Gamma) flow through your body and reach your brain. 3) Your body temperature is regulated by a "thermostat" in the brain ( specifically the hypothalamus, of which temperature regulation is just one of the functions). The chemicals released into the body due to infection will go to the hypothalamus and tell it to "raise the temp, we got bugs causing some shit somewhere. Cook em up". This causes a rise in body temperature from its normal resting temp to a higher one, which we call a fever. 4) Along with this, we have a function of the human body to regulate how our blood vessels work. Blood vessels can constrict and can expand depending on how much blood is needed in a particular organ. Blood carries white blood cells, red blood cells, basically everything you need to live and fight off disease, and it is *warm (*and blood cools itself when it flows through the skin to allow heat to dissipate). In certain conditions, such as eating, blood vessels supplying the skin will constrict in order to ensure more blood is sent to the gut to provide energy for digestion of food. In an infection, blood vessels keep more blood around the "vital" organs (heart, brain, lungs, etc) because these organs are a necessity for the body to function. This further increases core body temperature. 5) So now you have blood concentrated in the core organs internally and chemicals causing your thermostat to raise the temperature. The difference between the temperature between the internal organs and outermost organs (skin) is greater. This difference is what causes the feeling of "cold" as sensory receptors on and around the skin and other outer organs send signals to the brain via a spinal cord nerve tract called the "spinothalamic tract" that the difference between the environment and internal temperatures is greater. Think about when you go from inside your house in winter versus in summer. In winter, the outside temperature is lower than your internal temperature, thus you feel "cold". Where as in summer, the outside temperature can be greater than the inner temperature, so you feel hot. This difference is what is the cause of shivering. Shivering is one of the body's mechanisms to raise it's temperature via muscle activity. As muscles work they use energy from glycogen and other substances derived from the food we eat. This energy usage is not 100% efficient, and the un-used energy is given off as heat (Newton's law of thermodynamics). This is the body's way of attempting to heat the outer organs, as the skeletal musculature is closely attached to the skin via the subcutaneous tissue and fascia and shivering lets heat to flow out to the outer portion. Think about it. When was the last time you felt cold and then felt your liver or spleen or pancreas shaking inside you trying to stay warm? they don't. 6) Weakness and tiredness are also related to these mechanisms. When those chemicals (cytokines, Interleukins, interferons) are released, some of them cause weakness and tiredness as well. This has a very good purpose: when fighting an infection, the body wants you to use all your resources to overcome this infection as fast as possible. Weakness is there to ensure you do not do something dumb, like a boxing match or run a marathon, while fighting the infection. Body doesnt want to share resources for unnecessary activities. Tiredness is to promote sleep. During sleep, your body releases more chemicals (complement system, etc) to fight infection. basically your immune system is MORE active while you are asleep than when you're awake. Basically the body wants you to be in bed and asleep so it doesn't have to divert energy towards frivolous junk activities while it is busy slaughtering foreign pathogens.
You don't feel temperature itself so much as you feel change in temperature. You feel cold in cold weather because the air is constantly sucking your body heat out of your relatively hot body. In weather around 75 F° or so (I don't remember the actual temperature), the heat you're losing is the same as the heat you're generating, so you barely feel temperature at all. When you have a fever, however, your body is much hotter. This means you have more heat to dump into the surrounding air, so you'll feel colder than you normally would in the same air.
There is a great experiment that you can do at home: Prepare 3 bowls of water, one cold, one natural temp and one (kind of) hot. Put your left hand on the cold and your right on the hoy one and leave it there for a while. Then put both on the natural temperature one. For one hand it will feel cold, for the other hot.