You probably heard this one from your mother. You were about to head out into the cold, and she called out that you had better remember your hat. After all, you lose most of your body heat through your head. Even the U.S. Army field manual for cold-weather survival says that you absolutely must cover your head in cold weather because 40 to 50 per cent of your body heat is lost through your head.
If this were true, we could walk around in the cold in just a hat and no trousers. But that would almost certainly leave you much, much colder than going without a hat. And much more exposed. And in much greater danger of a fine for public indecency.
This myth probably originated in a military study fifty years ago, when scientists put subjects in arctic-survival suits (without hats) and measured their heat loss in extremely cold temperatures. Well, since the only part of their bodies that were exposed to the cold were their heads, that’s the part of the body from which they lost the most heat. Dr Daniel Sessler, Chair of the Department of Outcomes Research at Cleveland Clinic and an expert in hypothermia, says that if you repeated this study with the subjects donning only bathing suits they would not have lost more heat from their heads than from any other part of their bodies of proportional size. A more recent study from the US Army research environmental lab confirms that there is nothing special about the head and heat loss – any part of the body that is left uncovered loses heat. No matter what you leave uncovered, an exposed body part that is left out in cold weather will cause a drop in your core body temperature.