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We’ve all seen those comparison photos. Some president starts off with a full head of dark hair, and a few years later they’re totally gray.

But stress doesn’t really turn your hair white. At least, not the hair already on your head. It can help reveal gray hairs, though, by increasing turnover.

And scientists think it might just speed up the graying process a little, too. Each hair gets its color from melanin, a pigment made by specialized cells called melanocytes in hair follicles. You can have gray or white hairs because the hair itself, which is mostly a colorless protein called keratin, is manufactured by different specialized cells in the follicle, which are called keratinocytes.

And they tend to live longer than the pigment-producing ones. So hairs can keep growing, shedding, and growing anew, even if those little pigment factories have stopped production. How long your melanocytes last—and therefore when you “go gray”—is mostly determined by your genetics.

But your head doesn’t turn white the second some of those cells die. Since the follicles can’t alter hair that’s already grown, gray hairs don’t start to show until the old, colorful hair has fallen out, which usually happens every few years. But, if something makes your hair fall out faster—like, I don’t know, being massively stressed out—then it might seem like you’re suddenly graying.

Chronic stress is known to trigger telogen effluvium, a condition where a hair follicle jumps ahead to the final stages of its life cycle and the hair attached to it falls out. So instead of lasting years, hairs can fall out within a few months of a stressful event. The new hair starts growing again right away, so it doesn’t cause baldness.

And it doesn’t affect melanocytes, so for young people, the hair that falls out grows back its normal color. But if you happen to be at the age where the next hairs in line would be gray anyway, it can speed up that turnover. It’s not that the stress turned you gray—it just bumped your gray hairs to the front of the line.

That said, there is some research that suggests stress might make you go gray sooner. That’s because stress can increase levels of free radicals—atoms or molecules that have an unpaired electron, which makes them unstable and very reactive. They basically try to steal an electron from anything they run into, which messes with key components of cells.

A 2006 study found that too many free radicals can prematurely age cells because of their toxic effects on DNA, or even kill the cells outright—and that includes melanocytes. Other things known to increase free radicals in your body, like smoking, also happen to be associated with premature graying. But so far, no one has conducted a controlled experiment to conclusively demonstrate the connection between stress, free radicals, and the sudden appearance of gray hairs.

So stress might make you go gray. Or it might just reveal how gray your hair already is. Thanks for asking, and a special thanks to President of Space Matthew Brant!

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