In every issue of WebMD the Magazine, we ask experts to answer readers' questions about a wide range of topics, including some of the oldest -- and most beloved -- medical myths out there. In our January-February 2011 issue, we asked Richard Ingebretsen, MD, PhD, a wilderness medicine expert at the University of Utah School of Medicine, about the oft-spouted idea that we lose most of our heat through our heads.

Q: Mom always said to wear a hat in the cold because we lose 80% of our body heat through our head. Is that true?

A: Lots of people believe that but this pearl of motherly wisdom is FALSE. Here's why.

The head only represents about 10% of the body's total surface area. So if the head were to lose even 75% of the body's heat, it would have to lose about 40 times as much heat per square inch as every other part of your body. That's unlikely -- which has been borne out by tests of college students who lost the same amount of heat whatever the exposed area.

"The real reason we lose heat through our head is because most of the time when we're outside in the cold, we're clothed," says Richard Ingebretsen, MD, PhD, an adjunct instructor in the department of internal medicine at the University of Utah School of Medicine. "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."

"There's really no such thing as 'cold,' when you're talking about the body," Ingebretsen says. "There's always heat -- it's just a matter of keeping it in."