Myth or truth…do you really lose 40% of your body heat through your head?

It’s very likely that your mum once told you to “keep your beanie on, because you lose most of your heat through your head!”. This long-standing myth is thought to have originated in the 1950s, when a US military experiment concluded that 40 – 45% of your body heat is lost through your head.

The parameters of this investigation were flawed, however, and the reality is the only reason we lose more heat through our heads in the cold is because the rest of our bodies are clothed. This article will briefly analyse the science of heat loss through our heads and explain in some detail why the age-old myth is incorrect.

The Science Behind It

Without diving in too deep, understanding the science of heat loss through your head will help you keep safe and warm as you work or play in the cold.

Generally, heat loss from your body is proportionate to the surface area of the unprotected area. This is why it is unlikely your head, only representing 10% of your body’s surface area, would lose more heat than other parts of your body. If the myth was true, you’d be just as cold if you’d forgotten your beanie as if you’d forgotten trousers!

In an interview with Richard Ingebretsen, MD, PhD, a more recent experiment was discussed, which concluded the people in the experiment lost the same amount of heat, wherever the exposed area. In the US military experiment referred to earlier, men were bundled up in warm clothing and exposed to bitterly cold conditions without any covering or protection on their heads. While they certainly would’ve lost heat through their heads, being the only exposed part of their body, the same effect would’ve taken place if they had their heads covered but were missing a sleeve off their jackets – they probably would’ve lost 40-50% of their body heat through that arm!

Why its still important to keep your head warm

While the old myth is certainly incorrect, if you are working or playing in extreme cold temperatures, it is still important you protect your head, along with the rest of your body. There are several reasons for this;

• Your face, head and chest are more sensitive to changes in temperature than other parts of your body, so covering and protecting them makes you feel warmer, even if your body temperature isn’t actually any warmer.
• Your nose and ears are extremities and can receive less blood flow as your body temperature cools. This means there are vulnerable to cold injury, such as frost bite. Read more on this hazard in this article.
• There is less Insulating subcutaneous fat over your head than the rest of your body, so it can feel cold more quickly.
• Vasoconstriction is less effective over the head, which means your blood flow won’t slow so much as your body temperature cools, and you will get colder faster. This article goes into vasoconstriction in more detail.

In conclusion, the old myth that most of your body heat is lost through your head is incorrect.  Heat loss from your body is proportionate to the surface area of the unprotected area, so if you’re working in cold environments, its important you cover and protect everything, especially your extremities.