Wikipedia:Reference desk/Archives/Science/2025 October 31

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October 31

Half of body heat is not lost through the head?

List of common misconceptions about science, technology, and mathematics#Human body and health states:

• Half of body heat is not lost through the head, and covering the head is no more effective at preventing heat loss than covering any other portion of the body. Heat is lost from the body in proportion to the amount of exposed skin. The head accounts for around 7–9% of the body's surface, and studies have shown that having one's head submerged in cold water only causes a person to lose 10% more heat overall.

1. If "the amount of exposed skin" is where heat is lost, then in a situation where being cold is a problem (so, clothed), would a person not lose about half their body heat from their head (face and neck [or more if bald]), with the other half from their hands?

2. Would a mask like a balaclava (clothing) not reduce loss by about half?

3. If the hair on the head doesn't expose skin on the top of the head, does that mean wearing a normal hat doesn't help at all in preventing loss of body heat? -- Jeandré (talk) 06:38, 31 October 2025 (UTC)

References

1. If you read the sources cited, yes, that's what they claim. When warmly clothed for winter, a bit under half the heat lost is from the head -- and the research demonstrating that appears to also be how the "half" claim originated. The other half one could guess would be from hands and due to the fact that winter clothing doesn't totally prevent heat loss, only attenuates it. That information could conceivably be added to our article.

2. Probably somewhat less than half (since it will slow, not prevent heat loss from the head, and less than half the heat loss is from the head). But a significant amount, yes.

3. If you're already wearing a long sleeve shirt, does adding a winter coat not reduce your heat loss? A hat covers the ears (high surface area to volume ratio) and adds another layer of insulation to keep heat in. -- Avocado (talk) 12:58, 31 October 2025 (UTC)

Thermal insulation is never 100%, so any covered skin areas will nevertheless lose heat to a colder environment. If the surrounding air is completely stagnant, the air itself will form an effectively insulating layer. Assuming a light air flow that swiftly carries away the heated air, given a thermal conductivity reducing factor $\lambda$ of the skin covering (where $\lambda =0$ would mean 100% effectiveness), the heat loss as a function of the fraction $c$ of covered skin area is proportional to

$c\lambda +(1-c),$

in which the first term covers the contribution to the heat loss by the covered skin, while the second term corresponds to the contribution by the exposed skin. If $c=0.9,$ meaning that 10% (say head and both hands) is exposed, for the contribution of the exposed skin to be at least 50% we get

$\lambda \leq 0.111...,$

which means quite effective insulation, as for an Arctic expedition.

Thick hair reduces air flow and thus helps to keep one's head warm in cold weather.  ​‑‑Lambiam 15:53, 31 October 2025 (UTC)

This would need verification for accuracy but since it's somewhat related I thought it would be appropriate here. Apparently, because the brain and heart are vital organs, in case of hypothermia, other than the fact that limbs dissipate more, the body might limit energy and blood flow to them, in extreme cases potentially also resulting in cramps. I often heard the assertion that because of this, covering the head also helps to increase general comfort (including of the hands and feet)... 206.248.143.75 (talk) 20:03, 1 November 2025 (UTC)