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Inspired by several questions and answers here and also one at Biology SE, I have been looking around to try to find out whether this idea I heard constantly as a youth has any merit, or it just folk-wisdom gone bonkers. Usually expressed in the slogan given in the title- if you want to keep your feet warm (at night), wear a hat (to bed)- this counter-intuitive notion was repeated to me often by many I respected. My relatives, Scout Leaders, and others all believed this notion.

The explanation falls into one of a handful of broad categories, but the most common is that things like hearts, brains, and guts are very important, while things like fingers and toes, not so much. So when the body is in a situation where it needs to ration resources it might steal resources from the extremities in order to give a greater share to the vital organs. It does this by constricting the blood vessels in the extremities, reducing blood flow to those areas, and keeping more of the warm, oxygenated, nutrient rich blood nearer the core. This explanation seems to be confirmed in Causes and remedies for cold feet.

Another explanation I heard was that the majority of heat loss in the body is via the head. Some would continue by saying that heat rises, and the head in on top. I recall one grizzled old outdoorsman I encountered in college making all of us put our hands just over our heads and "feel the heat." But it seems this claim may not be due to physics, but that people tend to cover the body rather thoroughly when outside in the cold, except the head. So the heat simply has no where else to go. In reality, given uniform insulation, the body loses heat proportional to surface area. See, for example: Fact or fiction: Does wearing a hat keep you warmer? and the linked Biology question.

Of course, this may be exactly the source of my title's slogan in the case of sleeping - you are everywhere wrapped in an insulated sleeping bag, except your head. So when you add socks and blankets around your feet while leaving your head exposed, you aren't really helping.

Putting it all together, it is difficult to separate cause and effect, science and myth, and determine what exactly goes on in a body out in the cold. What, if anything, can one reliably conclude?

  • Found it very hard to find tags for this one. Feel free to edit. – cobaltduck Aug 15 at 12:15
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    For scientifically inclined answers you may want to ask this on Skeptics. Personally this is the first time I've heard about it. – gerrit Aug 15 at 13:01
  • @gerrit- Skeptics vehemently demands notable claims, so "heard it from a grizzled old outdoorsman" might not stand-up. But I will look around and see if I can find something more official, and consider that possibility. – cobaltduck Aug 15 at 13:03
  • If you've heard it from various sources then you should probably be able to find it repeated online (or in print), including in notable places. – gerrit Aug 15 at 13:09
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    One factor in heat loss per unit area is the blood supply. If you have ever had a cut on the head (say on the forehead) you might notice that it bleeds a LOT more than a similar size cut on your arm. There is a lot more blood a lot closer to the surface on the head. – Jon Custer Aug 15 at 14:30
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I'm trying to answer in a more empirical way than through scholarly articles but I think it's a good method to prove it to yourselves that wearing a hat does affect other body parts.

While there is a common agreement that your head isn't particularly special in terms of its ability to lose heat compared to other body parts, there is one practical experiment that anybody can do themselves to feel how a very small part of your body exposed to an extreme temperature can affect you whole body:

On a very hot day, during an activity that brings your body heat way up, go to a cold water body when you feel like you're overheating. Simply remove your footwear, keeping the rest of your clothing on, and dip your feet in the water. It should take barely a moment before you feel your entire body, including your head, cooling down. The blood flow getting chilled in your feet is recirculated, pulling heat away from the rest of the body.

The logical conclusion is that if your blood loses heat on an exposed body part, it will go back to other body parts cooler, thus cooling those body parts, or hampering your body's own heat generation in cold weather.

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A rough measurement shows that the surface area of one arm is about 1.7 times that of my head. So the rate of heat loss from my head will be around 1/3 that from both arms - quite significant.
But when it is cold:

  • My arms will be covered with good insulating material.

  • There will be a big wind chill on my head because it is exposed.

  • My body will give priority to essential organs, which includes the brain.

  • To do that it can reduce the blood supply to my limbs, making my extremities feel cold.

  • But it must increase the blood supply to my head to maintain its temperature.

By insulating my head as well as the rest of my body, more blood may flow to my extremities.
Ergo, by wearing a hat my feet will be warmer.

So in cold weather I wear a hat when outdoors, and if I get too warm the first thing I do is remove the hat. No science is needed - only common sense. It is obvious that to maintain your body temperature, all exposed skin should be covered.

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    The key thing here is that your body does not treat all parts equally. It 'knows' full well that without a functioning core (heart/lungs) and a brain (head), everything else is toast. So, when in doubt, the body will keep those things well supplied with blood. Your extremities (feet, hands, fingers, toes) get the short end of the stick. This is why you are trained to check temperature and feeling in the hands and feet as a wilderness first responder. – Jon Custer Aug 15 at 13:34
  • @JonCuster as I wrote, a cold head means its blood supply must be increased to compensate for the heat loss, unlike other extremities. – Weather Vane Aug 15 at 13:40
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    @WeatherVane I think they're agreeing with you. :P – Adonalsium Aug 15 at 13:52
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    @WeatherVane - sorry, didn't mean to come across as negative. More to support. It might be worth editing in the point that your body prioritizes your core and head at the expense of the extremities. You've got at least a 90% solution there. (As an aside, many years ago I complained to my scout master on a winter campout that my feet were cold in the morning. His solution was for me to take the empty 5 gallon water jug the half mile to the all-weather water tap, fill it, and bring it back. I didn't complain about cold feet again after that...) – Jon Custer Aug 15 at 14:22
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    While this may be true, it is presented in the question with references. As written it is just sharing as an opinion one of the two options in the question. I think the bar for a good answer to this question, is much higher then this answer is hitting. – James Jenkins Aug 15 at 14:31

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