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It may be different for other people, but for me, anything above 32°C (90°F) is very uncomfortable, and my body is inclined to seek cooler temperatures. But I would think that at 32°C, the body would have less work to do to get itself to 37°C. So why is it not comfortable in those temperatures?

My theory is this, but I don't know if it's right:

The body's abilities for warming itself are much more sophisticated than its abilities for cooling itself (which are non-existent, possibly?). So it likes to be in an environment 20-30 degrees below optimal because it can easily handle that. But up in the 32's and we're dangerously close to going over the optimal, and the body doesn't know how to get it back down after that, so we are inclined to seek safer temperatures.

Is it something like that?

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not all animals require this body temperature - mammals have made some good business of assuming their bodies will all be at the same temperature and then warming themselves up to the right temperature. as the others note there are biological warmers, but no biological refrigerators, so choosing a temperature above most weather conditions was a useful part of the strategy of being warm blooded ... –  shigeta Jul 21 '12 at 15:37
    
I refer you to the quora answer: quora.com/Temperature/… –  bobthejoe Jul 24 '12 at 7:46
    
I added more details. Check out! –  C Rags Feb 13 at 3:55
    
@reopen The question also asks the reason why the skin temperature is lower than the core temperature. This is not dealt with in the linked question –  C Rags Feb 13 at 3:57

4 Answers 4

up vote 7 down vote accepted

The body can never stop working. If the body stops working, you die. And while the body is working it cannot avoid generating heat. Being in an environment somewhat colder than the body makes getting rid of this excess heat easier, and is thus more comfortable.

The body's abilities for warming itself are much more sophisticated than
its abilities for cooling itself (which are non-existent, possibly?).

The body can cool itself down by sweating.

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Although in general this answer seems reasonable, I would like to see some references. What is the amount of heat generated by the body, say, when you're sleeping? Does it change during the day? Depending on the season? Is it actually that non-negligible (we are talking about a 16° difference here...) –  nico Jul 21 '12 at 7:05
    
It is quite a substantial amount of heat, and it is more when we are active so therefore more during the day. I don't have the resources available nor how to calculate those amounts. –  Hermann Ingjaldsson Jul 21 '12 at 8:44
    
Thermodynamically, your BMR goes nearly completely towards heat, as you do no work on the environment. I have a BMR of about 1800 kCal, so I need to lose all of that heat through my 2 square meters of skin every day. Some of that is insensible perspiration, and some of it is just conduction. –  Resonating Aug 14 '13 at 20:17
    
As a rule of thumb, a human produces roughly the same heat as a 100-watt light bulb. –  Russell Borogove Aug 14 '14 at 16:37
    
@RussellBorogove that is, slightly less than 100 watts? –  Jan Dvorak Aug 14 '14 at 17:56

Your body requires energy to function. Just like in a powerplant, the energy comes from oxidizing fuel (food, instead of coal or gas). The efficiency Of conversion is rather low, and results in excess heat, which must be rejected to the environment. When it's cool, the heat is easily convected to the surrounding air. When it's warmer, or you're producing more waste heat than can be rejected through simple convection, your body relies on evaporative cooling, i.e. sweating.

When it's very cold, the normal waste heat is not sufficient to keep you warm enough for normal bodily functions, so you shiver. This is physical activity which your body performs solely to create waste heat, which warms you up.

There's an article about muscle efficiency on Wikipedia, indicating that the human body is about 25% efficient. This means that about 75% of the energy consumed must be rejected as heat.

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It may be different for other people, but for me, anything above 32°C (90°F) is very uncomfortable, and my body is inclined to seek cooler temperatures

I think you've rather nailed the key point here. I'm going to deduce from your question that you live in a temperate country? Every year, foreign students from India come over to my university in Leicester, UK. Even when the temperature is, to us, unpleasantly hot they will be shivering in their coats and complaining it's too cold. Similarly, were I to go over to India I'd be suffering in the heat while they're thinking it's a lovely comfortable temperature.

So, I believe, the answer is nothing to do with the ability of the body to maintain certain temperatures - you'd need to go considerably above 32°C or below 21°C to reach temperatures the body can't cope with - but rather a question of acclimatisation. You find 21°C comfortable and 32°C comfortable because that is the temperature that you've become used to. You can probably even recognise this from your own experience: I'm sure you've experienced days in spring feeling delightfully warm when days of the same actual temperature in autumn feel unpleasantly cold.

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This is due to the fact that skin is the interface where heat is lost.

Our body due to constant functioning, produces heat constantly as a by-product (due to exothermic reaction of ATP break mainly). The excess heat needs to be conducted away from the body, or it will cause a decrease in the body metabolism to prevent temperature rise.

Heat is lost mainly through the skin by:

  1. Sweating - Through evaporation
  2. Radiation - As heat waves (IR rays - That's why IR camera captures people at night)
  3. Conduction - Directly through objects that touch skin
  4. Convection - Through air circulation

When the ambient temperature rises, the heat lost through radiation, conduction, and convection drastically decreases. And often when the temperature is high, there is a accompanying rise in the relative humidity which decreases the heat loss through sweating (as the amount of water vapor is high in the atmosphere, the sweat does not evaporate, so no heat is lost).

So the heat which is not lost is felt as the "hot sensation". It relieves by stopping any activity, seeking shade or a cool place, etc... all of which increases the heat lost or decreases the heat produced.


You have to note that the temperature of skin is lower than the body temperature.

enter image description here

The Skin temperature is lower than the core body temperature for two reasons:

  1. The skin acts as a medium through which the external temperature is measured - as such the skin temperature is at equilibrium with the external temperature. The brain regulates the core-body temperature in response to temperature measured through skin. If a person is exposed suddenly to cold environment, skin looses much of its heat in the form of radiation (radiation is direclty proportional to the temperature difference) this will cause perception of cold and the body starts shivering even though no actual heat loss has occured from the core body thermal load (only skin looses heat, not the body core). The brain anticipates that the core will loose its heat when exposed to such low temperature for prolonged periods and starts the warming mechanism before the actual cooling occurs such that the cooling is either prevented or minimized. This is called Anticipatory control and the temperature of skin being close to the ambient temperature within physiological limits is needed for this.

  2. Skin is the medium (almost the only medium) through which the excessive heat produced by the body core during activity is expelled. The skin temperature is lower so that a constant gradient can be created between the body core and body surface to maintain the flow of heat. (Heat losses through urine and feces is minimal)

For more details see this question. All the answers in this question are good and will increase your understanding of what actually happens.

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1  
+1 for teasing it all out –  Chris Stronks Jan 10 at 14:23
2  
Good answer Here –  rhill45 Jan 11 at 4:51

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