You lose 90% of your body heat through your head.

Not necessarily. You lose body heat through anything uncovered, according to Dr. Aaron E. Carroll and Dr. Rachel C. Vreeman, authors of "Don't Swallow Your Gum!: Myths, Half-Truths, and Outright Lies About Your Body and Health."

Your head is not special in that way — it's just more likely to be exposed.

"Most of the time when we're outside in the cold, we're clothed," Richard Ingebretsen, MD, PhD, told WebMD Magazine. "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."