Today let’s consider a perennially popular medical myth, one that continues to circulate year after year as temperatures begin to drop: that 45% of body heat dissipates through the head (we’ve even seen that figure as high as 80%). Although it is possible to lose a significant amount of heat from the scalp, the notion that almost half of the body’s heat is lost this way simply isn’t accurate.
This myth likely derives from a misinterpretation of a decades-old US military experiment in which subjects were exposed to extremely cold temperatures while wearing arctic survival suits. However, the suits only covered the subjects from the neck down. Therefore, naturally, the majority of the heat loss occurred by way of the uncovered head. This idea was then perpetuated by a 1970s edition of a US Army survival field guide that recommended covering one’s head in frigid temperatures because “40 to 45 percent of body heat” is lost through the head.
Since heat loss from any body region is largely dependent upon surface area, you can see why this belief isn’t logical, because your head comprises only about 10% of your body’s total surface area. Therefore, it’s probably more correct to say that about 10% of body heat is lost through your head—and that’s if your entire body were to be equally insulated.
In reality, the relative amount of heat you lose from your head will vary, depending on a few factors: the clothing you wear, your physical activity level, and the various bodily functions that govern temperature regulation. It’s true that there may be some situations in which one might lose a tremendous amount of relative body heat through the head, such as when it’s the only uncovered part of the body. But in general, the head isn’t a significant area of heat loss—at least not disproportionately more so than any other part of the body.