Do I Lose Most of My Body Heat from My Head?

Covering your head on a cold day is a no-brainer—but if you had to choose between wearing a hat or pants, it’s clear that this scientific-sounding saying is off the mark.

This health tidbit taught by parents everywhere seems to have originally come from the 1957 edition of the US Army Survival Guide. The military manual said that “40 to 45 percent of body heat” escapes through the head, although the original meaning has been taken out of context.

On a cold day, your head radiates heat out like a lantern, but this escaping warmth doesn’t add up to “40 to 45 percent” of your body’s heat loss—let alone most of it. When you’re naked, only about 10 percent of heat made by the body radiates from the head—far more is lost from the larger surfaces of the torso, arms, and legs. Only if the temperature is very low, and you are wearing thick insulated gear everywhere else, would the Army Manual apply—it described soldiers who were without hat or ear muffs but otherwise well wrapped up.

So Mom was right—but only if it’s colder than 25ºF and you are already wrapped up in good cold-weather clothing but foolish enough to not be wearing a hat.

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Head heat loss

The colder it gets, the more you need a hat. At 5°F, you would lose up to a bone-chilling 70% of your body heat from your uncovered head.