Why Do We Lose Hair From Our Head, but Not the Rest of Our Body?
WHY me?
As we get older, one of the biggest fears many people have is of losing all the hair on their head. In humans, males tend to lose their hair and go bald much sooner and more frequently than females, and baldness remedies and prevention has become a major industry.
However, the rest of the hair on our body doesn’t seem to suffer the same fate. Most men have arm hair, leg hair, and everywhere-else hair well into their old ages, once the hair on their head is long gone. Why is there such an unfair balance in men?
Well, the truth is, humans do lose their body hair, but based on the different genetic, physical, and chemical processes in the body, it’s hard for us to notice!
A Brief History of Human Hair
Human beings evolved from primates (monkeys), which are mammals, just like us. It’s important to remember that all mammals are covered in body hair (mostly in the form of fur). Humans, however, aren’t covered in fur for a number of reasons, namely that it makes it harder to cool the body. Our ancient ancestors, traveling long distances (perhaps while persistence hunting) in the hot summer sun, would have needed a way to cool their bodies as they moved. Sweating is the most effective form, which happens in the skin, which fur blocks. Therefore, humans evolved to fill their mobile needs by losing the fur over the course of generations.
That being said, primates and other mammals do experience thinning of the hair or hair loss, and in some primate species, they experience something akin to balding.
Why do we have hair on our head?
The hair on human heads has stuck around over millions of years for a different reason. Since the head is the part of the body most commonly exposed to sunlight (and the Equatorial sun of Africa while we were first evolving, no less), hair protects the scalp from overheating, and also reflects much of the UV radiation away from the head. The hair on the top of the head, the sides of the head, and the rest of the body are all slightly different, but we’ll get into that in the next section…
So Why Do We Lose Our Hair?
The hair follicles on our head go through what are known as growth cycles, where hair is grown and extended from a single site for 5-7 years. At that point, the hair will stop growing and fall out. That particular follicle will then “take a break” for a while, before restarting the entire process. most hair follicles can go through a handful of these growth cycles over the course of a lifetime.
A male sex hormone might be responsible, causing tightening of head tissue eventually impacting the hair follicles. Characterised by hair loss from the top and front of the head, 'male-pattern hair loss' is partly determined by genetics and partly by high levels of a male sex hormone called dihydrotestosterone (DHT).
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