Medical Mythbusters – Do you really lose 80% of your body heat from your head?

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True or False:  80% of your body heat is lost from your head.

FALSE!!

I love this one. My mother must have used it on me a million times growing up to get me to wear a hat, which I would not do since I grew up in the 70s and my Farrah Fawcett hair would have been ruined.

Where did this “80%” come from? Apparently from a weak US military study done in the 1950s that examined heat loss from Arctic volunteers dressed from neck to toe in survival gear. Duh, their uncovered heads lost more heat than the rest of their bodies. Were I to go outside in the bitter cold naked (as awful as that image is to contemplate) 100% of my body heat would be lost from my whole body. A slightly higher proportion of the heat might be lost from my head thanks to the greater blood supply to the head and face, but the head doesn’t have a lock on heat loss.  If you go outside in a pair of shorts you’re going to lose a lot of heat through your legs.

What my mom was worried about, of course, was the dreaded frostbite, of Jack Frost nipping at my nose. What exactly would put my nose (or ears or toes) at risk?

Environmental: Prolonged exposure, extreme cold, damp cold, high altitude. During severe cold, frostbite can develop in a matter of minutes. Everything that is exposed is at risk.  Feet and hands are affected most frequently, but ears, noses, cheeks, and even corneas are also at risk.  I challenge you to find a hat for your cornea.

Poor underlying health and/or altered mental status: Prior cold injury, alcohol use, tobacco use, malnutrition, diabetes, peripheral vascular disease, and severe mental health all limit the body’s ability to respond to any severe stress, including cold temperatures. Of note, prior cold injury can quadruple the risk of a subsequent cold injury.

Clothing: Inadequate clothing obviously increases exposure. But constrictive clothing that limits blood flow to the extremities, toes, etc. also increases risk of cold injury.

Being male: Whether this is because of some kind of genetic susceptibility or because males tend to spend more time outdoors isn’t clear.  African American males appear to be at special risk.  During both the Korean and Falkland Wars, there was a higher prevalence of frostbite in African American men than in other similarly attired races.

The bottom line? Mom was right, especially if you’re a male who likes to train for marathons during sleet storms at very high altitudes in super tight clothes while crazy drunk and smoking like a chimney.  So…

  • Minimize exposure, especially if it’s extremely cold and/or damp. Higher altitudes (like ski trips) warrant even more caution.
  • Wear sensible, warm, non-constrictive, layered clothing.
  • Stay dry.
  • If you’re going to be out in the cold, avoid drugs, alcohol, and tobacco.

Victoria Rentel MD (OSU SHS)

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