Do You Lose Half of Your Body Heat from Your Head?

Claim
You lose half of your body heat through your head, making it the most important part of your body to cover in frigid temperatures.

Origin
The earliest reference of this comes from the U.S. Army Field Manual in the 1950s, which claims that “40% to 45% of body heat” is lost through the head. Since then, this has been a favorite bit of wisdom that Midwestern mothers and fathers repeat to their kids every winter.

Facts
This theory was revisited in 2006 and again in 2008. In the 2006 study, subjects were placed in cold water, sometimes with their heads above water and sometimes with their heads submerged. Scientists found that the head accounts for about 7% heat loss, which is proportional to the amount of skin that’s showing.

The 2008 study corroborated these findings, saying that about 7% to 10% of body heat is lost through the head. The reality is that the amount of heat lost from a given part of your body is relative to how much skin is showing. If it were true that half of your body heat exits through the head, then it’d mean that you lose roughly 20 times as much heat per square inch as every other part of the body.

“If you don’t have a hat on, you lose heat through your head, just as you would lose heat through your legs if you were wearing shorts,” said Dr. Richard Ingebretsen in an interview with WebMD. “There’s really no such thing as ‘cold’ when you’re talking about the body. There’s always heat—it’s just a matter of keeping it in.”

Takeaway
The U.S. Army Field Manual got this one egregiously wrong, but not everything from their cold weather survival section is bunk. One thing they did get right is that fingers, toes, nose, ears, cheeks, and chin are the first places to get frostbite, so use your melon and prioritize covering those areas instead.

Sources
Survival Guide — The Army
Do We Really Lose Most of Our Heat Through Our Heads? — WebMD
Frostbite — Mayo Clinic
Festive Medical Myths — The BMJ