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What are the higher heat loss areas of the body and how can I reduce heat loss in those areas?

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3  
a head - it is good to take a cap a with you when sleeping under the sky, even in summer. –  Tomas Jan 29 '12 at 22:37
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7 Answers

up vote 8 down vote accepted

My original answer to this question sparked a surprisingly intense debate, so I'm rewriting it to clarify a few points and offer a more holistic answer.

Let me start by saying that every square inch of skin on the human body is capable of allowing heat to escape. That is to say, if you wear a jacket with no pants, your legs will lose more heat than your torso -- but if you wear pants with no jacket, your torso will lose more heat than your legs. Both areas are capable of losing heat -- and will do so more quickly when exposed. Therefore, any part of your body that's more exposed to the cold than another part has the potential to lose more heat than other than parts that are less exposed.

This is fairly obvious, but I mention it for completeness' sake. This generally means that you should try to cover yourself as much as possible, especially larger skin surfaces like the torso.

However, the point that I think the OP is trying to get at is that -- all else being equal -- every square inch of exposed human skin does NOT lose heat at the same rate. That is to say, some areas of skin lose heat faster than others. If you were to stand in the cold totally naked, some parts of you would lose heat more quickly than others. This is an indisputable, biological fact. Allow me to explain:

Human blood serves many functions -- one of which is thermoregulation. As an evolutionary adaption, humans have areas on their body that are especially suited for releasing heat, in order to cool us off when we get too hot. In these areas, there is a high volume of blood flow, and that blood passes very close to the skin. These areas are:

  • The skull
  • The groin
  • The armpits
  • Some might also say the extremities, like fingers and toes.

In these areas, there is a lot of blood flowing around, and the skin is fairly thin, allowing heat to escape from the blood more quickly than in other areas.

Therefore, if you are in a desperate survival situation where you risk hypothermia, these are the areas of the body you should focus on keeping the warmest.

Armpits are fairly easy to keep warm, just keep your elbows down and they'll be insulated by your torso and upper arm.

It's important to keep warm, dry underwear in order to keep your groin warm as well.

And yes, YOU SHOULD WEAR A HAT. While you might not lose the "majority" of body heat through your head, it is one of the areas of skin that loses heat most quickly and it should be one of the main things you focus on keeping warm.

The extremities are also important to keep warm. I have friends that go out jogging in the winter wearing shorts and a t-shirt. They don a warm beanie and gloves right before they go out, and those are all it takes to keep them warm in freezing temperatures.

In summary: If you have clothes or ways to protect every inch of skin on your body, you should do that. I thought this was basic common sense, but people were squabbling so I'll reiterate.

However, if you only have limited means of protection and you need to focus on warming only a small area of your body, you're best off focusing on the four areas listed above.

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guardian.co.uk/science/2008/dec/17/… -- "The face, head and chest are more sensitive to changes in temperature than the rest of the body, making it feel as if covering them up does more to prevent heat loss. In fact, covering one part of the body has as much effect as covering any other." –  Russell Steen Jan 31 '12 at 21:57
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This one indicates that this is not nearly so clear cut as you imply. Heat loss is based on skin temperature, which the body can regulate, but tends to be higher (and thus lose more) in the torso, not the head. ncbi.nlm.nih.gov/pmc/articles/PMC1086117/pdf/pnas01858-0029.pdf –  Russell Steen Jan 31 '12 at 22:03
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Not available online but these show that the heat loss through the head is relative to the % of exposed skin, not anything special about the head. The head loses heat consistent with its portion of total exposed skin area (ie, at the same rate as other skin) Vreeman R, Carroll A. Seasonal medical myths that lack convincing evidence. BMJ 2008 ; 337 : a2769 (20-27 December). & Collins KJ, Abdel-Rahman TA, Easton JC, Sacco P, Ison J, Dore C. Effects of facial cooling on elderly and young subjects : interaction with breath-holding and lower body negative pressure. Clin Sci 1996 ; 90 : 485 - 492. –  Russell Steen Jan 31 '12 at 22:11
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Heat loss can occur from anywhere on the body through a number of processes:

  • Conduction e.g. when sitting on the ground.
  • Convection e.g. due to wind chill.
  • Radiation i.e. heat loss direct to the environment from exposed skin.
  • Evaporation i.e. heat loss through perspiration.

Other factors:

  • Metabolism generates heat; conversely, without enough sustenance the body won't generate heat.
  • Respiration the body moistens and warms the air on inhalation, this heat is lost on exhalation which increases the colder and dryer the air is.
  • Body size the smaller the body the greater the relative surface area to lose heat through.

Combat heat loss by:

  • Minimising exposed skin, which will radiate heat.
  • Wear wind-proof clothing to minimise convective heat loss.
  • Use a sit mat or sit on your rucksack when taking a break to prevent conductive heat loss.
  • Wear moisture-wicking undergarments to minimise heat loss by evaporation.
  • Eat high-energy foods to keep your metabolism up.
  • Breathe through a scarf in cold dry air.
  • Monitor children and be aware that they will feel the effects of cold before you.

As for specific, high heat loss, areas of the body, it depends:

  • If you are sitting on a rock or camping without ground insulation the high heat loss areas will be those in contact with the ground through conductive heat loss.
  • If your back is sweaty under your rucksack, heat loss through evaporation could make your back the high heat loss area.
  • Cold, dry air can make respiration a high heat loss area.

In general, the high heat loss areas will be those not adequately protected from the various mechanisms of heat loss prevalent to the situation you are in:

http://www.guardian.co.uk/science/2008/dec/17/medicalresearch-humanbehaviour

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This addresses heat loss in general, but doesn't really answer the OP's question directly -- what parts of the body to concentrate on warming. –  Hartley Brody Jan 29 '12 at 2:40
    
@HartleyBrody -- All parts lose heat evenly. How else could Graham answer this then? There is no single part which should be focused on because heat is lost through the skin uniformly. There was an interesting experiment done on this where people were submerged in ice cold water. I'll see if I can find it. –  Russell Steen Jan 29 '12 at 22:29
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Alright, I kind of feel like giving up at this point since I'm getting so trashed for it, but "heat is lost through the skin uniformly" is not true. The OP's question indicates that they know this, and are asking where it's lost the fastest -- but all of the answers neglect this. –  Hartley Brody Jan 29 '12 at 23:26
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Yes, heat loss can occur from anywhere, but the question asks where it goes the fastest. –  Hartley Brody Jan 29 '12 at 23:31
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I say good answer to the wrong question –  mjrider Jan 30 '12 at 17:01
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It's probably worth pointing out that a lot of people reading this question may be thinking along the (commonly quoted) line that about 80% of body heat is lost through the head - which is much more of a myth than people realise (See here for details.) From what I remember, it was an experiment done with people fully kitted out apart from the fact that they weren't wearing anything on their heads... and, somewhat unsurprisingly, most of the body heat lost in this scenario was from the head.

Of course, it is important to keep the head wrapped up, but it's equally important to keep other parts warm - especially the torso. Even though extremities may feel colder, this is because your body is reserving the heat for its vitals and cutting it off more to things such as your hands and feet. Warm up the core of your body and it'll start warming your extremities as a result!

In terms of how to reduce heat loss in those areas, it's generally as simple as wrapping up as warm as you feasibly can (and as much as is appropriate for the conditions. Obviously full arctic gear isn't required for a damp autumnal day!)

In short, wrap up as best you can all over, but it's especially important on the torso. In practice though, it shouldn't come down to deciding what to wrap up in particular - if it's cold, wrap up as best you can all over!

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@downvoter - Could you explain the reason? –  berry120 Jan 29 '12 at 22:53
    
I didn't vote down but again this doesn't answer the question...(but I think this question is turning into an argument REAL fast) –  mjrider Jan 30 '12 at 21:10
    
+1 Increase your covered area (i.e. pants if wearing shorts, jacket if wearing a t-shirt, hat if bald). Add wind layers if it's windy. Add insulated layers to as much area of your body as possible if neither of the previous bits work. –  Ryley Jan 30 '12 at 21:24
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PS: my sources tell me that heat loss through your head is pronounced if you are already shivering. –  Ryley Jan 30 '12 at 21:32
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To answer the question directly, the three areas that lose heat the fastest are actually:

  • The Head
  • The Groin
  • The Armpits

This is why those are the areas that naturally grow the most hair on human bodies. It's an evolutionary adaption to keep us warm. In those areas, there is a lot of blood flowing and it passes very close to the outer layer of skin, allowing it to cool of more rapidly and lower our body's temperature. It's all of the blood rushing around your skull, into your legs, or into your arms, respectively.

Covering your head is a no brainer. As others have mentioned and most people already know, the head it where you lose most of your body heat, so wearing a dry, windproof hat with a lot of loft is always a smart idea if you're cold.

The groin and the armpits are a bit more tricky. If you're dressed according to normal human social standards, you'll probably be fine. But if, for some reason, you're out in the cold with little or no clothing, those are the areas to focus on the most.

Keep your arms tight at your sides and cover your groin with your hands. Not only is that our natural reaction to the whole "being naked" thing, it also happens to be the best way to stay warm with no clothes on!

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This is wrong. The myth of heat loss through the head has been debunked and if hair on the groin and armpits was essential for insulation we would have evolved soft downy hair growing from birth not coarse hair growing from adolescence. –  Graham Jan 29 '12 at 13:59
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My source for this is mostly my father, who is a doctor. Also, the "head" claim is backed up by my friends who go running in the winter in shorts and a t-shirt: they put on a hat and gloves and those are enough to keep their entire body warm. While the head may be generally over emphasized in thermal regulation, it's still a very important source of heat loss. It's dangerous to have someone who just read the wikipedia page on thermoregulation proselytizing about the "wrong" ways to stay warm –  Hartley Brody Jan 29 '12 at 16:00
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I suspect the reason people who go running in shorts and t-shirt need a hat is there is very little muscle around the top of the head so this part of the body gets cold, whereas the rest of the body is kept warm by the muscles they use when running. –  Phil Jan 29 '12 at 16:33
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"The head is one of the areas that loses heat most quickly. I'm not saying anything about whether it's most of your heat"... "As others have mentioned and most people already know, the head it where you lose most of your body heat" That's exactly what you said - or at least strongly implied, whether you meant to or not! I agree that the head should be kept warm - see my comments on chat for more info. The biggest problem in my mind is that you're implying (whether you meant to or not) you should concentrate on keeping the head warm above the torso, which I don't believe is sensible! –  berry120 Jan 30 '12 at 19:44
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If it's an indisputable biological fact I'm sure you can easily cite a dozen studies showing such. "Indisputable scientific fact" is usually the refuge of someone without actual evidence. guardian.co.uk/science/2008/dec/17/… –  Russell Steen Jan 31 '12 at 21:52
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here is a pictorial answer to try and figure this out! I believe this is a un-clothed male under a thermal camera (SFW)

enter image description here

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I think that guy is bald :) –  Ryley Jan 30 '12 at 21:15
    
This is interesting. Since I'm so invested in this answer, do you have a source with more info on what the image shows, how it was captured, etc. –  Hartley Brody Jan 30 '12 at 21:43
    
/*dont tell anyone*/ but this is just a google search for a thermal camera image of human body but en.wikipedia.org/wiki/Thermography –  mjrider Jan 30 '12 at 21:49
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I think I saw that guy at LAX –  LBell Mar 21 '12 at 11:58
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Lots of ways to reduce heat loss: Wear a hat scarf and gloves as these keep the most important parts of your body warm. Wear warm knickers (even if you're a guy). You can get fleecy knickers but not fleecy pants. Also, you can huddle, like penguins as it reduces your surface area and conserves bodyheat.

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I like the take on huddling together - good emphasis on the fact that there's ways other than clothing to stay warm. –  berry120 Sep 12 '12 at 21:31
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OK, answer me this: Two men go out in -10 below weather on a lake to ice fish for the day. They are wearing identical clothing, jackets, gloves, etc., and the only difference is one is wearing a winter cap and one is bareheaded. Which one will be colder after 3 hours? Wearing a cap outside in Winter is just common sense, IMHO, and anyone says it's all bunk, has never gone ice fishing for a day in cold weather in Minnesota.

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If you take any two people in identical gear for warmth and give one of them a single extra piece then yes, that person will be warmer. I could replace the word "cap" in this answer with "sweater", or "socks", or just about anything and the person with less clothing will be colder. Try going on your ice fishing trip with a cap and no shirt. Take a friend who has a shirt and no cap. Let us know how the common sense for cap wearing works out for you when you get back. –  Russell Steen Dec 31 '12 at 20:31
    
I do not believe you answered the question. The OP was asking which areas of the bodies are most important. Your response is more like 'everything is important'. –  theJollySin Jan 2 '13 at 18:42
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