Losing body heat. Which part of the body loses heat most quickly? Is it true that you lose most of your body heat through your head? Which organ produces the most heat in the body? Is a hat the most effective means of keeping warm in cold weather?
A common statement is, “It’s easier to keep the heat in, rather than to keep cold out”. Many assume that body heat disappears upwards and especially through that big brain of yours.
Origins of the Myth
This medical myth can be traced back to the 70s and the US military handbook for survival in harsh conditions. According to this survival guide, 40-50% of the body heat evaporates through the head, and the book advises the soldiers to wear a hat to keep warm.
As a more modern version of the manual (2002) states, the cold itself may not be the biggest threat but rather the effects it has on the human ability to function properly: “Cold is a far greater threat to survival than it appears. It decreases your ability to think and weakens your will to do anything except to get warm. Cold is an insidious enemy; as it numbs the mind and body, it subdues the will to survive”.
Even in the modern version from 2002, the myth prevails:
“For example, always keep your head covered. You can lose 40 to 45 percent of body heat from an unprotected head and even more from the unprotected neck, wrist, and ankles. These areas of the body are good radiators of heat and have very little insulating fat. The brain is very susceptible to cold and can stand the least amount of cooling. Because there is much blood circulation in the head, most of which is on the surface, you can lose heat quickly if you do not cover your head.”
It sounds reasonable and logical but it’s actually a myth.
Your head contains a lot of blood veins and arteries. It is reasonable to assume that when this part of the body is exposed to cold, it can cool down the whole system quickly. But as it turns out, what is important is how much the overall body temperature drops. If the rest of the body is well insulated and warm, your body will keep a constant hot temperature even if your face is exposed to cold temperatures. A sleeping bag is consequently a very effective method of staying warm in a safe and secure manner. In harsh conditions, your ears could still get cold damage, but you will survive as long as the rest of the body doesn’t drop to dangerously low-temperature levels.
Debunking of heat loss myth
One reason people believe more heat is lost through the head is simply that we are more sensitive to changes in temperature in the face and the area around the nose. This leads to the sensory feeling that cold is actually more cold than it is, because we have a “temp radar” (thermoreceptors) in our face, which tracks even small changes in temperature.
Humans feel that heat evaporates from the face more quickly than the rest of the body. This, in conjunction with the “dive reflex” of many mammals, including humans, triggers a reaction in the body which switches the blood supply to focus on the most vital parts, the brain, the heart, and the lungs. Bloodflow is effectively shut down for arms, legs, and other less critical organs. The extremities of the human body are also designed to cope with oxygen deprivation and more extreme temperatures without being damaged.
This myth was also proved wrong in this BBC article:
“In other words, we don’t lose most heat from our heads. The results show that having your head immersed in cold water only adds 10% to your overall heat loss in a cold pool. And given that the head accounts for 7% to 9% of the body’s surface, that doesn’t seem excessive.”
What research is the myth based on?
The Guardian explains this in an article about this myth here. It most likely stems from a poor scientific study by the US army during the 1950s. People were dressed in arctic survival clothes and exposed to freezing weather. The only part of their bodies left uncovered was the head. Consequently, most of the heat was lost through their heads. But as long as the rest of the body keeps a healthy heat level, it does not really matter which part of the body is exposed to cold, or through which part of the skin the heat sips out.