One of the funniest misconceptions often still taught today

Especially in certain countries (which isn't surprising because the spread of misconceptions is strongly tied to local word-of-mouth culture and customs) even to this day it is taught that a person loses most of their body heat through the head. Sometimes no exact figure is given, but when it is given, 80% seems strangely common. This is supposed to teach how important it is to wear a hat during cold weather, especially in sub-zero temperatures. It's also commonly repeated as a factoid even in other situations.

As you might have guessed, this is just a myth. In reality a person loses about 10% of their body heat through the head. Which isn't surprising because the surface of the head comprises about 10% of the total surface of the entire body. Which, of course, means that there's nothing special about the head compared to the rest of the body in this regard.

The interesting part is where this myth originates.

The most plausible origin of the myth is an experiment and study made by the United States military some time in the earlier-20th century. In this experiment they tested how much body heat is lost by military personnel wearing arctic suits in sub-zero temperatures. They measured that from all the body heat emitted by the soldier's body, about 45% was emitted from the head.

Which, of course, is a lot higher than 10%. Not nearly as high as the often-cited 80% figure, but still significantly higher.

The figure, however, starts making sense once you realize that when the test was performed, the army arctic suit didn't have any sort of warm headgear, so the soldiers were either not wearing any headgear at all, or only a helmet, which obviously provides very little protection against heat loss.

The 45% figure happens when wearing thick winter clothes without headgear. It doesn't indicate how much a naked person loses heat from their head.

And even then, it's just 45%, not the often-cited 80%.

As a result of this study the military started issuing warm protective headgear alongside the rest of the arctic suit. And, somehow, this result got widespread among the general public and changed via word of mouth until it reached the modern misconception.