Everyone’s heard of testosterone – it’s a hormone that makes you hairy, right? Correct, but that’s not all testosterone does. As part of the androgen group of hormones, testosterone also effects the voice breaking, muscle and bone strength and the development of male genitals. What a busy hormone!
But let’s focus on hair growth for the moment. How exactly does testosterone make you hairier?
Once testosterone is made (from two other steroid hormones, progesterone and progenolone) it whizzes off around the body looking for receptor sites to stick on to. These receptor cells hang out in a specific area of the hair follicle called the dermal papilla; the testosterone binds on tight and, dependent on genes, either encourages or discourages hair growth. Testosterone can even help you grow hair on one body part and stop you from doing so in another – nope, we don’t know why and nor do the clever science people. It’s a mystery (probably genetic, though).
The body has two types of hair follicle; vellus and terminal. Vellus hairs are the fine, almost invisible ones, and terminal ones thicker, longer and darker. Hair changes from vellus to terminal as it goes through its growth cycle – the presence of increased testosterone, for example during puberty, is what makes this happen. As we age, however, the reverse sometimes happens and the big, strong hairs regress into tiny fine ones again – eventually dying and not growing back. Explains why our elderly relatives never have to bother shaving.
Fun fact about testosterone: the more testosterone someone is exposed to in the womb, the greater their ability to grow a beard. Doesn’t mean they won’t go bald, though; baldness is the result of low testosterone which can happen at any age.