Rough day today? It may show up in your hair three months from now.
Stress is known to cause hair loss, and the life cycle is so predictable that you can set your calendar to it, according to a report by The Atlantic.
In his new book, “Hair: A Human History,” dermatologist Kurt Stenn reveals that the growth phase of a single strand of hair can last from two to six years. (That's just on your head. “Other hairs have much shorter growth phases — an eyelash’s, for example, is 30 days,” Julie Beck wrote for The Atlantic.)
Hair has four phases: anagen, when the hair grows; catagen, a brief period when the follicle shrinks; telogen, a rest phase; and exogen, when the hair, unappreciative of all your expensive shampoos and conditioners, takes leave and clogs your bath drain.
"This process is always happening, and it’s totally normal for a person to lose between 50 and 100 hairs a day this way. That’ll plug your drain up, but compared to the 90,000 to 150,000 total hairs on the average person’s head, it’s pennies," Beck wrote.
But stressful events like a divorce or job loss interrupt the process, for reasons scientists don't completely understand. They do know that stress causes something akin to a stampede — call it panic at the follicle disco — and larger-than-usual numbers of hairs will rest, then fall out en masse — up to 10 times more than the usual rate, according to Stenn.
"This has been shown in mice, when the stress of being exposed to loud noises led their hairs to go into catagen prematurely," The Atlantic reported.
"In human hair, this delay lasts three months, the combined length of the catagen and telogen phases. It’s like clockwork," Beck wrote.
It's so predictable, in fact, Stenn told her, that when patients complain to dermatologists about hair loss, the first thing the doctors ask is, "What happened three months ago?"
Of course, stress isn't the only thing that causes hair loss. Giving birth does, too.
Most new mothers lose hair several months after having a baby, thanks (or no thanks) to decreasing estrogen levels, the American Academy of Dermatology says.
Simply getting older causes hair to thin, too, and a study published last month in Science says aging stem cells are to blame. "Over time, they found, the stem cells accumulated genetic errors that led them to not be able to rejuvenate any longer. This in turn caused hair follicles to shrink," Leah Samuel wrote in STAT.
Samuel interviewed Elaine Fuchs, a professor of cell biology and development at the Rockefeller University in New York, who was not involved with the study but offered this depressing assessment: “Once the hair growth cycle goes, it goes,” Fuchs said. “Once hair loss is triggered, it’s a self-propelling event.”
Scientists are hopeful, however, that with these new discoveries, they might find a way to slow or reverse the process before the stem cells start to go.
And just because you're getting older, there's no need to panic and start shopping for wigs. Donald Trump turns 70 in June, and he's still got plenty of hair. Or so he says. Only his hairdressers know for sure.