what is hair?

A scientific look at the stuff, and why we have it.

by Douglas Main
22 June 2017, 4:30pm

i-D Hair Week is an exploration of how our hairstyles start conversations about identity, culture, and the times we live in.

This week we're celebrating hair, but we'd be remiss if we didn't pause for a second to consider what it actually is, and what it's for. Luckily, we can explain! And it might even give you a new appreciation for how strange and beautiful a thing human hair can be.

Hair is made of a protein called keratin, which is also the main component of your fingernails. (And, incidentally rhinoceros horns.) This protein is produced by follicles, bulb-shaped structures within your skin. You're born with all the follicles you will ever have, about 100,000 of them on your scalp alone, or about five million in total covering your body. You cannot produce new ones, and when people go bald or lose hair, the cells within the follicle die and quit producing keratin.

The hair itself is produced in the bulb deep within the follicle, and as it passes through it is coated in oil from sebaceous glands. This oil helps keep the hair from being damaged by water and the elements, and makes it shiny. (Of course, too much oil isn't desirable, but without these oil glands your hair would be brittle and dry.) Pigment cells in the follicle give hair its color, and these pigments are all varieties of the chemical melanin, which is also responsible for making skin dark.

Within the follicle, each bit of hair starts out as a living cell. But through a process called keratinization, the cells fills with fibrous material and dies, becoming hair. (Your hair isn't living, of course, though it once was, and thus getting a haircut doesn't hurt.) The hair itself is made up of the elements carbon, oxygen, hydrogen, nitrogen, and sulfur.

Just like us, each follicle cannot be on all the time. Each one goes through cycles of activity, during which it continually produces hair, before going dormant, during which times the hair falls out. On average, you lose about 50 to 100 hairs each day. Body hairs go through this process in the time span of about a month, whereas scalp follicles can be on for years at a time. Men's hair grows slightly faster than women's, but women's follicles have lengthier growing cycles, explaining why female hair grows longer.

Compared to other types of growth going on inside the body, hair grows extremely quickly. Head hair, for example, grows about six inches per year, though this varies according to each person and their genetics and diet. Only the marrow cells within your bones, which are important for regulating your immune cells and keeping you healthy, grow more quickly than hair.

The texture of your hair is determined in large part by the shape of the follicle, according to the American Academy of Dermatology. Oval-shaped follicles, for example, produce curly hair, while straighter hair is the progeny of more round-shaped cells. The shapes these take on are highly influenced by genetics, and can also change over the course of your life. Indeed, many babies have far different hair from what they have later in life.

None of this answers another important question: What is hair for?

The primary purpose of hair in mammals, including humans, is to keep warm and protect the skin. However, hair also has the important role, at least in other animals and possibly in humans as well, of broadcasting pheromones. These are smelly chemicals produced by the body that give clues about each individual's well-being and sexual compatibility. The role and importance of human pheromones is a matter of current scientific research and debate, though it could help explain why we still have pubic and underarm hair, which help "broadcast" these smells into the world.

As you've probably noticed, humans' most impressive domain of hair occurs on the head. But this is a curious fact, considering that the vast majority of the 5,000-some other mammals species are hairier, and that we are the only (mostly-)hairless primates. At some point, our ancestors lost their hair, an important event in human history that forced us to invent clothes.

One theory as to why humans lost our fur is that it allowed us to stay cooler, specifically to keep our large brains from overheating. Humans are actually "prodigiously good sweaters," Nina Jablonski, a professor of anthropology at Pennsylvania State University, tells The Independent. And we got this way by losing hair and increasing our number of sweat glands, which don't function as well in hairy areas, because hair absorbs fluid. Smooth skin, on the other hand, allows it to evaporate and thus drain heat from the body. However, hair on the head is still important for warming the head and protecting it from the sun's rays. As your parents told you, much of the body's heat—about one-third—is lost through the head.

Another theory as to why humans become less hairy is that it allowed us to stay free of parasites like lice, which can spread serious disease, University of Reading researcher Mark Pagel writes in Scientific American. He theorizes that having less hair became an attractive feature to the opposite sex. "Smooth, clear skin may have become a signal of health, like a peacock's tail, and could explain why women are naturally less hairy than men and why they put more effort into removing body hair," he writes.

Hair also serves as good biological "advertisement" for one's self, as it reflects much about your genetics and health. And that's powerful, both biologically, and perhaps at a deeper level. Even ancient myths speak of the power of hair. The tale of Rapunzel can be interpreted in part as a story about hair's ability to allure, connect and even deceive; on the male side, Samson's hair (from the Bible) ends up being the source of his mystical strength. So wear your hair how want; it speaks volumes, as even biologists and mystics can agree.


Text Douglas Main
Photography Olle Svensson via Flickr 

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