National Geographic
Hair loss isn’t life-threatening, but that doesn’t mean that it can’t be life-changing. For many people, losing hair is tantamount to losing themselves.
“People go through grieving,” says geneticist Angela Christiano of Cornell University. “It’s grieving your appearance… for many people, it’s grieving identity.”
Hair loss is incredibly common. According to the American Hair Loss Association, two thirds of American men will experience noticeable hair thinning or loss by age 35. At 50 years old, that figure rises to 85 percent. And though it’s less often spoken about, plenty of women lose hair, too: about 40 percent of people experiencing hair loss in the United States are women.
Despite its ubiquity, hair loss is not as well understood as you might think—especially among people who are not men, who were the subjects of the majority of past research. Experts discuss the biology of balding: who experiences it, why it happens, and what we can do about it.
Testosterone and balding
Even millennia ago, there were hints that balding had something to do with male sexual development; ancient Greek philosophers and physicians noted in their medical writings that eunuchs don’t go bald.
Scientists now understand that male pattern baldness—by far the most common cause of balding in men—happens thanks to androgens, or male sex hormones. Unfortunately, research owes that knowledge to a cruel period of American history. In 1942, anatomist James Hamilton studied people with mental disabilities who were castrated as part of the eugenics movement. Hamilton discovered that men castrated before puberty never developed male pattern baldness, except if they were treated with testosterone.
Hamilton’s studies also produced a classification scheme for male pattern baldness, which is still used today to score degrees of androgenetic alopecia (pattern baldness).
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How male pattern baldness works
Scientists think that male pattern baldness has to do with a hormone called dihydrotestosterone or DHT (about 10 percent of the testosterone in the body is converted to this more potent form daily). Oversensitive follicles on the scalp react to DHT by shrinking down and spending less time in the growth phase of the hair cycle, says Andrew Messenger, a retired dermatologist at the University of Sheffield in the U.K. This leads hair to thin and fall out.
Puzzlingly, follicles on the back and sides of the scalp tend not to react to DHT this way. This leads to the distinctive “pattern”: a receding hairline and balding on the crown and vertex of the scalp.
Also, androgens have the opposite effect practically everywhere except the scalp: in humans and other animals, androgens tell hair to get thicker, darker, longer. That’s why men tend to grow more visible body hair and beards after puberty.
Hair loss in women and children
Somewhere between one third and half of women will noticeably bald in their lifetimes. The most common cause is female pattern baldness.
Pattern baldness in both sexes share some similarities, and male and female pattern baldness have the same medical term: androgenetic alopecia. However, it’s still unclear whether or how androgens are involved in female pattern baldness. In general, researchers know a lot less about female pattern baldness, says geneticist Stefanie Heilmann-Heimbach, who studies the genetics of balding at the University of Bonn in Germany.
“It’s a classic example of a field in which almost all of the clinical research was done on males,” says Christiano. Specifically, research has focused on white men—a bias with links to the pseudoscience of phrenology.
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As in male pattern baldness, female pattern baldness causes terminal hairs on the scalp to shrink down. But instead of balding from their temples and over the crown of the head, women tend to lose hair diffusely from all over their scalp. This thinning tends to first become visible at the part and then spread outwards.
Pattern baldness usually strikes both men and women as they age, though it tends to start later in women (around age 40 or later, while men often notice balding in their 30s or even younger). But teens and even children can lose their hair, too. One major cause is alopecia areata, an autoimmune disease that attacks our hair follicles. It affects about one in 50 people.
Because kids, teens, and younger women tend not to lose hair as often, balding can be especially traumatic for them, says Christiano, who started studying the genetics of hair loss after experiencing alopecia areata herself.
Inheriting hair loss
Male pattern hair loss is very genetic, says Heilmann-Heimbach. “Estimates from twin studies are that it’s at least 80 percent heritable.”
You might have heard that male pattern hair loss is inherited through the mother’s side. But that’s an oversimplification, says Messenger.
Though one important gene involved in balding, the androgen receptor gene, is located on the X chromosome, there are also over 350 points in the genome that have been implicated, says Heilmann-Heimbach. Most of them aren’t on the sex chromosomes.
The genetics of female pattern baldness are more opaque, as is the relationship—if any—between female and male pattern baldness.
Can balding be stopped?
People concerned about their hair loss have options. “There’s treatment with medicines, and there’s treatment with surgery,” says Christine Shaver, a hair restoration surgeon at Bernstein Medical – Center for Hair Restoration in New York.
Modern hair transplants follow one of two methods: follicular unit transplantation (FUT) or follicular unit extraction (FUE). Both move hair follicles from a donor site, usually the back of the head, to other places on the scalp—processes that rarely work well for anything except male pattern baldness.
Medication can be helpful even for patients considering hair restoration surgery, says Shaver, as having more remaining hair makes a transplant easier. However, while most hair loss drugs stop pattern baldness from progressing, they don’t usually regrow hair.
There are currently two FDA-approved medications for male pattern hair loss: minoxidil, which you might know as Rogaine, and finasteride, which hinders the conversion of testosterone into DHT.
Finasteride can have serious and potentially long-lasting psychological and sexual side effects, and the U.K. issued an alert this year advising doctors to carefully inform and monitor patients taking the drug. Shaver says that finasteride can work in women but it isn’t approved by the FDA for this purpose. It also carries significant risk for women, including elevated risk for breast cancer. “Many post-menopausal women will take finasteride and find benefit, while acknowledging risks,” she says.
Shaver says the first step in seeking any treatment should always be getting a formal diagnosis from a board-certified dermatologist. While male pattern hair loss is the most common cause of balding, there are many reasons why people lose hair—and most cannot be reversed effectively with FUT or FUE. Shaver also cautions people seeking hair loss surgery to be careful about choosing an experienced and accountable provider.
“I have many people walking in the door thinking that their hair loss is genetic and they’re going to get a hair transplant,” she says. But after diagnosis, “I unfortunately will have to deliver news that hair transplant is not the best approach.”
Still, not everyone who experiences hair loss decides to treat it, and medical insurance rarely covers it. “Skeptics will say, well, how do you even call [pattern hair loss] a disease? How is that not just the normal pattern of hair miniaturization with age?” says Christiano. Many people make their peace with balding, and even learn to love their new look.
