‘Always keep your head covered. You can lose 40–45% of body heat from an unprotected head.” That’s the advice in a 1970s US Army Survival Manual, which is probably where this myth originated, says John Tregoning, a professor of vaccine immunology at Imperial College London.

The reality is that there is nothing special about your head. When you go out in the cold, you lose more body heat from any area you leave exposed than from those parts protected by clothing. Out in a snowsuit but no hat? You’re going to lose heat quickly from your face and head, while the suit slows down the cooling of your body.

“But if you went to the Arctic in a swimming costume, you’d lose more heat from your legs than your head because their surface area is bigger than your head’s,” says Tregoning.

Nevertheless, there remains some discussion about whether the head is more susceptible to heat loss. Tregoning points to a British Medical Journal article from 2008 which suggests that because you’ve got less fat on your head than the rest of your body, it is slightly less naturally insulated. The article also argues that vasoconstriction – the narrowing of blood vessels to conserve heat – is less effective on the head.

Overall, though, Tregoning says, “the head does lose heat, but it’s not uniquely heat-losing. There’s a study where researchers put peoples’ heads in cold water,and then looked at the speed of cooling down, and it wasn’t particularly faster than anywhere else.”

Still, he says, if it’s very cold and you’re not wearing a hat, you are going to get cold – just as you would if you went out without a jumper on. “People probably need to cover their face as well, if they can. You lose quite a lot of heat through your face.”