October 26, 2004 By ANAHAD O'CONNOR
THE FACTS: Put on a hat, parents tell their children before sending them outside on bitter winter days. While that might be sound advice, the popular belief behind it — that most of the body’s heat escapes through the head — is misguided.
The amount of heat released by any part of the body depends largely on its surface area, and on a cold day you would lose more heat through an exposed leg or arm than a bare head.
Dr. Daniel I. Sessler, an anesthesiologist and expert on hypothermia at the University of Louisville medical school, said the popular myth stemmed from military experiments conducted five decades ago. In those studies, he said, researchers dressed subjects in Arctic survival suits and exposed them to frigid conditions. But the suits only covered the subjects from the neck down, he said, so naturally most of their body heat escaped through their heads.
That isn’t a fair comparison, Dr. Sessler said. If you did the same experiment with someone wearing a swimsuit, only about 10 percent of the heat loss would come from the head.
The body responds to cold temperatures in at least two ways. One is the constriction of blood vessels in the arms and legs, reducing blood flow to the extremities. This protects the brain and vital organs in the trunk but leaves the fingers and toes susceptible to frostbite, in effect sacrificing them. Another response to cold is shivering, which generates heat.
The face, head and upper chest are up to five times as sensitive to changes in temperature as other areas, Dr. Sessler said. This creates the illusion that covering up those areas traps in more heat, but clothing another part of the body does just as much to reduce overall heat loss.
THE BOTTOM LINE: The body does not lose most of its heat through the head.