I've been discussing with some friends the idea of your head being a major source of heat loss or not. Somehow I've gained the impression that your first goal for warming up should be to add insulation to your torso (regardless of your current state of dress - i.e. even if you were completely naked or already completely clothed). Others argue that putting on a hat would be the single more effective addition (in this case, assuming you were already wearing clothes).

I'm pretty sure the source of my idea came from some of Mr. Nisley's posts, where he tended to treat the hooded and non-hooded versions of clothing items as the same, except that since the hooded version covered 7% more body area, it was therefore 7% more effective. Was that just a simplification for us, or is it really that simple??? i.e. is the key to heat loss just covering as much body area as possible, or are certain areas significantly more important?

If you brain gets cold you start making bad decisions, and then you die.

Cold fingers, toes, arms, and legs aren't as severe.

It could get be even more complicated if you factor in natural insulation that may or may not be present on said head.

Your head puts out about the same amount of heat per square inch as the rest of your body. That being said, if your head is the only exposed portion of your body (which is often the case), it may then be your major source of heat loss since the rest of your skin is not losing heat very quickly (due to it being insulated).

I believe keeping your torso warm is most important because that is where your major organs lie. If they start to get cold, then your body will body will try to keep them warm by restricting flow to your extremities. At least that's how I understand it...

Eric - that's a good point, if you have a giant curly head of hair, adding a hat could actually be negative? :)

John - you sound so certain about this - "Your head puts out about the same amount of heat per square inch as the rest of your body." I agree, but I'd really like to know how you came to this conclusion...

The guy I'm talking to is mentioning things about how there are clusters of blood vessels near the skin in your head, armpits and groin. It seems somewhat convincing that you would lose more heat from those areas if that was true...

Ryley,

The physiological factors that are a result of slow onset hypothermia, such as vaso constriction of the limbs but, not the head, have been explained by me in a number of posts. For one example, see http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=13697 and reference the one dated 5/21/2008 00:53:41.

I said "about" because it's probably not 100% exact.

See here for a couple of examples:
http://well.blogs.nytimes.com/2009/06/29/11-health-myths-that-may-surprise-you/
http://www.guardian.co.uk/science/2008/dec/17/medicalresearch-humanbehaviour

One interesting quote: "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."

Richard - sorry, I read that thread, but only skimmed the second post. Duh, sorry.

That's the info I was looking for exactly. What isn't quite perfectly clear is how you know so d%mn much about all this! :)


John - I like that quote!

Ryley,

I answered the same question a little simpler two months after the prior post I referenced. See http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=15085, on 07/31/2008 13:01:45 MDT

If we're talking about blood exposure to cold, I would be most concerned about the neck, where the carotid arteries run close to the surface, with virtually no fat insulation, and carry huge volumes of blood.

One way to stay warm is to wear wrap around eye glasses.

Most the head is surrounded by bone (some of have hair also, I don't). You can loose a lot of heat from your eyes.

Bradley,
I've been shaving my head for years. Since I first did it I can tell that I have more fat in the back of my neck and generally on my head. This might be the body's reaction to the lack of hair.

Edited by dextersp1 on 01/30/2012 15:22:32 MST.

Richard - one clarification then. It seems like there is not an exactly one to one connection between exposed body surface area and heat loss. You mentioned in that other thread that "When not shivering, the heat loss from the head’s 7% body surface area is ~10% of the body’s total heat output". How are you getting from 7% BSA to ~10% heat output?