Fact or Fiction: "If you want to keep your feet warm, wear a hat." (and the various explanations for it)

Question

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?

Answer 1

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.

Answer 2

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.