Do you wear a Fu Manchu? Sideburns? A soul patch? If so, you may attribute your ability to grow facial hair to your hormones.
Sex hormones called androgens, which promote the development of male traits, are the main reason why men generally grow facial hair and women generally don’t. We’ll get into why in a moment, but first a warning: hair follicles aren’t as simple as they seem. For some, androgens stimulate hair growth. In others, they reduce it (hello, male pattern balding!). And in others — say, in the ear canal — androgens grow hair, but on a delayed schedule, decades after the same sex hormones trigger a beard to sprout.
Why this follicular diversity? The answer is complicated.
“The reality is that it’s still quite challenging for researchers right now to definitively answer that,” said Ben Miranda, a consulting cosmetic and hand surgeon at St Andrew’s Center for Plastic Surgery & Burns and visiting professor at Anglia Ruskin University in the UK, “but there are differences within the hair follicles themselves that are preserved depending on the part the body They come from.”
That’s your face to androgens
Before puberty, the hair follicles on the body produce vellus hair, the light-colored, fine short hair you might see on the back of a woman’s hand. During puberty both men and women produce more androgens testosterone and dihydrotestosterone. However, the male body produces many more androgens. These androgens stimulate hair follicles to produce darker, thicker hair known as intermediate hair, the “peach fuzz” that’s usually first seen on the upper lip. Over time, androgen simulation encourages the production of even darker, thicker “end hair” of the same type seen on the scalp.
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The androgens do this by increasing the time a given hair follicle spends in its growth phase relative to its shedding or resting phases, according to Miranda, who also leads St Andrew’s Anglia Ruskin Research Group, a joint effort with St Andrew’s and Anglia Ruskin, Live Science told.
The hair on the female body also changes during puberty, but not as dramatically as in men. The hair follicles on a woman’s face near the ear transition from vellus hair to intermediate strands, and armpit and pubic hair transition to terminal hair.
Masculinizing Hormone Therapy, sometimes used by transgender Individuals, has a similar effect on body hair. Within a few years of starting testosterone therapy, body and facial hair become darker and thicker, according to the University of California, San Francisco (opens in new tab).
Follicles have gone wild
Still, the story isn’t as simple as “just add androgens.” In fact, in some scalp follicles, androgens promote exactly the opposite pattern as in body hair. Instead of triggering a transition from vellus hair to intermediate hair to terminal hair, androgens trigger terminal hair to become intermediate hair and then induce a transition from intermediate to vellus hair. It’s called androgenetic alopecia, better known as male pattern baldness. Not all men are genetically susceptible, but in those who are, the result is thinning at the front of the scalp that gradually creeps backwards with age.
“The really weird thing is, why is it that a hair follicle on the scalp that’s in one area is androgen sensitive and the one next to it isn’t?” said Miranda. “It just doesn’t make sense.”
The differences are specific to the body site where the hair follicle is developing; If you transplant a non-androgen sensitive follicle to a bald spot on the scalp, the hair will grow happily. (That’s why hair transplantation works.) But the reasons for these differences are hard to understand, Miranda said. The genes in each follicle are the same, but the way they control gene activity — an area called epigenetics — is markedly different. There are complex differences in cell signaling, or the cascade of molecular instructions, that cause a follicle to grow, rest, or fall off, Miranda said. Some genes become more or less active during balding, but research has not always found consistency in these genetic patterns.
“It’s epigenetic differences, up and down regulation of signaling pathways, exogenous exposure to different environments, hormones circulating in the body during these times,” Miranda said.
Miranda and his team are working on developing hormone-sensitive intermediate hair follicles that can be kept alive in the laboratory to study these factors. This research could help not only prevent the common pattern of male pattern baldness, but also treat some forms of alopecia, or loss of hair on the head and body, and hirsutism, a condition that causes women to be abnormally fat in the face and body become hair. Hair follicles also share their androgen sensitivity in common with the cells of the prostate, remarked Miranda. Under the influence of androgens, the prostate can enlarge or become cancerous, a very common condition in older men. Studying how androgens affect cellular processes in the hair follicle could help uncover how the same hormones cause prostate problems as we age.
Originally published on Live Science.
https://www.livescience.com/32700-why-do-men-have-facial-hair-but-women-dont.html Why do men have facial hair but women don’t?