There are many angles to look at, but it’s not ever complicated.
There are many conflicting and parallel mechanisms and situations, but still, when properly understood, each issue is pretty simple.
On the way, many examples may teach us handy insights on how to avoid that we and our loved ones will be too cold or too warm or die.
Quickly, we retract when something could seriously burn us, even before we become aware of the beginning hurt. But, we’ll only treat temperature control. Damage control from burning falls outside of our scope here.
Most of this stuff is written about the healthy body. Your situation may be different because of an ailment. Don’t use this (or any other) text instead of seeing and listening to a competent physician who checked you out.
Body Temperature in Humans
A healthy human will try to keep the body’s temperature at 37 degrees Celsius. Almost all biochemical reactions in the body (and their helpful enzymes) are calibrated to work best at normal body temperature.
Only sperm production goes wrong at that temperature. The body tries to keep the testicles at 35 degrees. (Avoid tight underwear or trousers.)
Every 10 degrees Celsius that our temperature is lower than the ideal, our biochemical processes get halved in speed. (So, 30 degrees less is 2x2x2=8 times slower or 12.5% of the normal pace.) A small child (they cool off quicker) under cold water or snow may therefore survive a time without oxygen that would have killed a larger person in warmer circumstances.
It has happened that doctors cooled down a patient’s body. This, to win time by slowing down destructive biochemical reactions in the body. People greatly cooled-down may seem dead. See below how to save them.
Sick is Not Broken but Different Settings
Microbes who would like to live in our bodies also multiply best at our normal temperature. (So many viruses and bacteria will never do well in our bodies, especially those that prefer plants. Therefore, generally, spoiled animal produce is more dangerous to eat than vegan foodstuff that went off. (Yet, funguses (on grain, peanuts) can be deadly.)
So, microbes targeting animals, including humans, thrive at 37 Celsius. When the body detects an invasion, it perks up the thermostat to 38 or even 40 Celsius, starting a war against them and creating immunity. (We ignore here other causes of fever.) Fevers make you feel sick and lethargic and lose your appetite (drinking enough suffices) so that you won’t waste energy the body needs to fight off the bug. They keep you in bed, prevent you from spreading the malicious germ everywhere. Strangely, chemically pushing down the fever with over-the-counter poison for your comfort doesn’t seem to slow down recovery. What does that imply?
Healthy people will easily produce a (high) fever when infected. Sick, old, and young people may have a serious infection without (hardly) any fever.
Temperature graphs that make no sense may indicate tampering with the administration or thermometer to feign illness in self or child in their care.
From Where Does Our Heat Come?
There are up to half a dozen sources for our body heat. Let’s go over them.
By-product of our biochemistry. Our chemistry may produce the molecules it needs for movement, creation, replacement, healing, and maintenance, but all generate heat as a by-product. Particularly, flexing our muscles.
Generated to get rid of calories. If your spouse at night is too hot to handle, ask them to eat fewer calories, even (especially) if they are not fat.
Overeating may result in overheating, fasting in being cold. A speeded-up metabolism may make you hot, while slowed-down, it may make you cold. Drinking hot drinks may warm your hands for holding the mug but likely not your body; the sugar and activity to take up ice cream will warm you.
Some folks feel cold when sleepy. Is that their metabolism slowing down?
When we eat stuff that makes our blood sugar level sky-rocket (refined sugar or flour, potatoes, beans, sweet foods, etc.), the body has no choice but to store this as fat, quickly. Other calories coming in at that time, also will be stored like that–if there are still empty fat cells. (The ability to create new fat cells is only in our baby time. Keep babies lean–but not hungry!) If you have no more vacant fat cells or your body is unaccustomed to such a peak in calorie intake, the body will speed up the bowel passage (to reduce uptake) and begin burning the excess.
(If you know that your room, bed, body, or partner may be hot during sleep, drink extra before you retire. Even if that would force you to visit the bathroom at night (an extra time). Better too much water (to shed) than too little, giving a headache from dehydrated. Water absorbed into food, like pasta and rice, and in plant cells, stays longer in the body. Black tea, coffee, and alcohol block the kidneys from retaining fluid, shedding liquid your body needs. Drink extra water to compensate for the loss.)
Generated to heat up the body. When the body is too cold, it will burn calories to heat it up, on top of the background by-product heat.
Shivering. This is a great trick. Muscle activity generates much heat. When we are cold (or when we need to make more heat to have a proper fever), we may shake (muscle movements) uncontrollably to generate more heat.
From outside of the body. A warm or hot environment may warm us up. The arteries in our skin open up from the warmth, and the blood going through it may warm up. But our surroundings may be so hot that we can’t get rid of the body heat that our body generates as a by-product of its functioning. Then the issue becomes how to cool down.
How do we Cool Down?
The body has two main ways to cool down.
Cooling the blood in our skin by exposing it to mild or low temperatures. Dressing lightly may enable us to get rid of our intrinsic body heat.
Cooling the blood in our skin by perspiring. Evaporating liquid takes energy and leaves the surface it covered colder. Sweat and other moister are wasted when they drip off of us. They work best when they form a thin layer on our skin, ready to disappear into thin air.
When our surrounding temperature is close to or over 37 degrees, we can only cool down by fluid evaporating on our skin. We may have to drink 5-10 liters of water per day to have enough fluid to keep sweating. When it’s very hot, the sweat evaporates fast so our skin won’t feel wet. We must remind ourselves to drink constantly to not dehydrate and overheat.
No sweat: When there is no wind. In my youth, the Apollo ‘space’ flights were the big sensation. But when my father was at that age, pole journeys were the big hype. He told me that they could shower outside without getting cold because there was no wind there. So their skin was first warm from the water and after the shower warm from the sun shining on them.
The body will also cool down when our metabolism slows down, but that’s often not an option to fight any overheating.
How Can we Get Too Cold?
Not sheltered enough. When we lose too much heat because it’s too cold.
Not enough food. The body will not just waste energy burning stuff it first had to store if food is on its way. But when its intake is delayed, it will.
Small children have a large skin surface relative to their body volume. (They also have less body content than grownups to generate heat.) This enlarged surface means that they cool off more quickly. Give them your coat. They suffer more and this gesture transmits empathy and generosity to the next generation. And they don’t understand what is happening while you can brave the cold knowing you’ll be fine and it’s over soon.
However, we may not at all be cold/hot and still feel cold/hot, or be cold/hot and still not feel cold/hot–read on.
Where do we Feel Our Warmth?
Our sense of how warm we are is in our skin. “I feel cold/hot” means: my skin detects too much coldness/warmth. This is important to remember.
Our Core Temperature Takes precedence
Yet, our body is more interested to guard its core than skin temperature.
When we sleep, our metabolism is lowered–though we may still warm up if we just ate abundantly. Lying in bed, our warmth will warm it. Then our skin arteries open op and we will feel warm. When our core is cold, more heat will be generated. When our core is warm, skin arteries and sweat glands will open to cool us down. The body has no priority for keeping the skin’s temperature comfortable. We need to take care of that by adjusting our surroundings’ temperature, our clothing, and the bed’s covers.
When there’s a lack of heat or blood to transport heat to the skin, first, the skin of our ‘extremities’ will turn whiter and cold: nose, ears, fingers, toes.
Consequences of Only Feeling Skin Temperature
The temperature control center in our brain checking blood temperature also may signal that change is needed. However, we cannot feel what it registers or does. We only feel what our skin communicates to our brain. When our skin is warm, we feel warm; when it is cold, we feel cold.
When we ate a lot of food, our intestines need more blood. If we then are in a cold surrounding, there may not be enough blood to keep our skin comfortably warm. Loosen your belt but tighten your coat. (I don’t know if that’ll help because a surplus of food means heightened burning, heating us up, but there may still be not enough warm blood to dispatch to our far skins.) Also, a heart that can’t keep up may be felt as cold extremities.
When we are making a fever, the body begins by closing the skins’ arteries to concentrate the core’s heat. We’re building a fever but feel cold. Maybe even with ‘chills,’ ‘cold’ shivers (to generate heat). When we take our core’s temperature, we see it going up. When the body core is heated up and our furnace is burning high, the skin vessels open up and we feel hot.
Some say that our hands or feet may stay cold when we’re not relaxed.
Some people, when they give someone with warm hands a cold hand, say: “Sorry for my cold hands,” while others say: “Oh, you hands are so warm.”
Your feet may have gone numb from cold, but your partner’s skin won’t.
Females have more of their fat under the skin. This puts more of a heat barrier between their internal body heat and skin. Therefore, generally, women will be colder more quickly. It’s sexist not to take that into account.
Some people exaggerate with the house’s thermostat. They make it in summer so cold that by such a temperature in winter we would have put on the heating, and in winter so hot that by such a temperature in summer we would have put on the air-co. It does give the feeling of being rich to waste so much electricity. The old Jerusalem system was, in summer, the windows open at night and in winter, in the day. Won’t work everywhere.
I learned the hard way (by experience) that it is OK to save money and not heat you whole house if you are mostly in one or a few rooms, but that it is is a wrong priority to be so frugal that you cut down on heating to save money and live in the cold. Being too cold, you can’t function well.
Being terrified may restrict the blood vessels in our skin, with or without perspiring, and being embarrassed may make the blood vessels in our skin open (blush), with or without perspiration. Feeling hot or cold from fear doesn’t mean we are. But the change in blood flow through our skin and the shivering, signs of healing old fears, may change how warm we actually are. (These processes may generate more urine, needing us to rehydrate.)
Losing or Gaining heat?
Besides us not being aware of our core temperature, we have no sensor to tell us, awarely or unawarely, if we are losing or gaining heat. For this, we must use our brains. When my feet are cold, I need to dress warmer so my feet may warm up again. (Cover your head for warmer feet!)
When it’s cold and we are cold, and we take a hot shower, after that, we feel nice and warm, even when in the nude in the same cold surrounding. However, while we are feeling warm, because of our warm skin, our body is losing heat via our skin and we’re actually cooling off–we just don’t feel that yet. So, while you feel nice and cozy, put on your clothes quickly.
Small children are harder to convince to put on warm clothing before going out in the cold. They feel fine and put on the coat when they are cold. But then they have lost precious warmth already. Try to explain it.
Drinking alcohol will make one feel warm while losing heat. (A grownup on land is hardly in danger of dying from cold unless drunk.) The Internet says that smoking does the opposite, restricts the peripheral blood vessels. I see so many people smoking who are less well dressed than the rest on a warm day because they need to perspire more to get rid of their heat?
More Incorrect Perceptions
The skin heat sensors actually easily confuse hot and cold. What we feel is therefore often given by context. When we expect hot, we experience the sensors playing up as signaling excess heat; When we expect cold, we interpret a neural temperature signal from the skin easily as too cold.
An example: When we take a hot shower and someone holds an ice cube to our neck, we feel it as a burning cigarette.
The sensors are also not objective. When our hands’ skin has really cooled off, and we put our hands under a stream of warm water, the nerves will scream: burning, scorching! (This could also be from the sensors un-numbing, still yelling about how cold it was but confusing it with heat.)
When the skin is too cold, temperature signaling goes numb. That’s why entering a body of cold water feels terrible until the blood vessels in the skin are closed (to preserve the body’s heat) and the sensors went numb.
Two Distinct Mechanisms Control Body Temperature
The temperature control center in our brain may signal that blood vessels in our skin should open or close more, to help adjust the body’s core temperature. When too high, the skin gets red to get rid of heat. When too low, the skin gets whiter to concentrate the heat inside. It may also tell the body to generate more heat.
However, there is also a feedback mechanism inside the skin. When the skin gets too warm, it becomes red, trying to get rid of body heat. When the skin is too cold, it will turn whiter to conserve body heat.
So, the sensors for the body checking our temperature and signaling heating up or cooling down are both in the skin (and we feel their output) and in the brain (whose signals we don’t feel). Yet, the body is mostly interested in regulating the temperature of the internal organs although we only feel warm or cold in the skin.
Now we get the big paradox: Keeping the core temperature stable has the greatest priority but the skin sensors have a greater impact than the brain. If there is a conflict, the priorities of the skin override the brain’s needs.
Paradoxical Consequences of the Stronger Local Mechanism
Fans and wind may help us cool down by hastening evaporation of sweat. A fan to help us cool down works better when its airstream is not directed at the same skin all the time. Because blowing off the air makes the perspiration to evaporate and the skin to cool down, closing its arteries, no matter the general need to have the body lose heat. Moving the blowing to other skin gives the former a chance to reopen its blood vessels. When the fan returns there, there will be fresh blood in the skin to be cooled off.
Fallen into an ice hole. Then the brain says: Too cold, close skin’s arteries. When rescuers put the victim’s skin in warm water, the arteries will open up, and the body gains warmth. Good scene. But, when the under-cooling is severe, reheating has to be done slowly, professionally. Otherwise, the cold peripheral blood may storm to the core, creating real havoc there.
But heatstroke. Then the brain says: Much too hot, open up all the skin arteries. But if rescuers put the skin in very cold water, the arteries will close and the core temperature will rise even more. This may kill the patient. The treatment is to put such a person in a bath of 36, 37 degrees.
Sunbathing. When we lie in the sun, we see very clearly how local skin perceptions override any central body interests. The side exposed heats up, turns redder (without burning), and starts perspiring, The non-exposed side turns whiter and cold. That side we could use to cool us down but it won’t because the cold will hinder blood circulation in the skin there.
The local mechanism is so strong that it may even kill us. When we are hot, all the blood vessels in our skin are open. When we then jump into a cool body of water, all these blood vessels close abruptly. That closes the door to a major part of our bloodstream from a fast-beating heart. When the blood doesn’t find a way out, the blood pressure abruptly rises so high that it forces the heart to stop contracting. Thus, perfectly healthy people with perfectly healthy hearts may kill themselves through cardiac arrest.
Talking of contracting skin blood flow, socks that are too tight may hinder skin blood circulation and actually make your feet cold, not warmer.
Most of the above, I learned in Medical School, 40 years ago. Not much seems changed. It’s hard to find all the above information in one place.