Yes, we can reverse gray hair. No, we don't know why it works. Just chill.

There are so many news stories this year that seem likely to give us gray hairs, you'd be forgiven for missing one that gives us hope that we can restore those gray hairs back to their regular color — no dye required.

In the first published study to find evidence of "natural re-pigmentation," researchers at Columbia University set out to create a computer model of how hair graying happens with age and in response to stressful events. First they identified 323 proteins that tell us whether a hair was gray, white, or colored at any point in its history. Then they snipped colored and gray hairs from 14 participants who listed and rated the stressfulness of their life over the past year. We know that there's a connection between graying and high stress; you only have to look at the hair of ex-presidents who don't dye it to see that in action.

What we didn't suspect is that the reverse may also be true; that de-stressing events can bring the color back to those exhausted fibers. That's what the study found when it matched the protein history of the hairs (which grow at a pretty reliable one centimeter per month) with the history of their owners: some normal-colored hairs had actually been gray in the past year, but went back to normal when life stress was low.

"I was not surprised by any of the stressors that correspond with graying; I was surprised to see how strong of an impact a vacation had on the reversal of graying," says Ayelet Rosenberg, lead author on the study. "One participant went on just a 2-week trip, and amazingly enough, five of their hairs regained color afterwards."

Examples of dramatic reversals in hair color across the body, in the Columbia study. Credit: elife sciences

Before the battered tourism industry celebrates this news, however, there's a lot still to nail down about the science of hair graying. More studies are needed to find out if this re-coloring effect ever happens over the age of 40 (it didn't for the few over-40s in the Columbia study). Still, if we can replicate these results soon — and the pandemic has given us one heck of a stressful event to map on hair around the world — the implications are huge.

Why? Because we're told constantly that too much stress is a killer, and we should combat it with mindfulness, exercise, sleep, and the rest of the familiar list. But the danger feels distant because it's internal. Nobody wakes up in the morning and sees their calcified arteries staring back in the mirror. When it comes to new gray hairs, though, many of us seem to zero in like Terminators.

And just this one time, human vanity might save us — because in our future world of preventative medicine, new gray hairs are actually worth telling your doctor about.

"Hair is unique, because it is a visible change that also indicates changes happening on a cellular level," Rosenberg says. "The ideal outcome would be for doctors to one day be able to use hair pigment as a diagnostic tool, using our method. If somebody did have a sudden onset of gray hairs, it would be worth looking at their stress levels that correspond to that point in their life.

"When you see it with your own eyes, I think people are more likely to care, and possibly make a change."

The stem cell solution

So what is actually going on at a cellular level when our hair regains color? Simple: Stem cells swinging into action. The raw material of the growing human body that can make any kind of cell required, stem cells are increasingly used in a wide range of medical therapies. We're in a golden age of stem cell research; just in the past few weeks we learned about how they could eradicate HIV, make brain tumors stop growing, and can be injected to successfully treat heart and lung disease in mice.

But hair is a relatively new area of focus for stem cell research, partly because we had no idea they were powerful enough to re-color our grays. Melanocytes are the type of stem cell that live in our hair follicles. Some studies suggest there is a limited reservoir of melanocytes up there; when they're done, so is your hair color. But this is hardly settled science.

"The depletion of stem cells would imply that the graying is permanent, but this has only been shown in mice," Rosenberg says. Melanocytes may also be replenished by mystery visitors, she adds: "Some transient stem cells may come in, which could possibly be responsible for the re-pigmentation that we are seeing here." Say it with me now: More study needed.

So fear not, forty-something millennials on the cusp of a graying decade. Science may soon find that extreme commitment to de-stressing can reverse hair color loss at any age — something that would be a lot easier to prove if those Buddhist monks that experimenters love to study (whose brains appear to be kept significantly younger by meditation) would just stop shaving their heads.

Or we may develop new stem cell therapies to restore our melanocytes in later life. Such a therapy may be open to abuse if younger grayhairs use it to mask the stress indicators they should be telling their doctors about in the first place. But either way, our new awareness of our hair's ability to recolor itself may be a blow to the $23 billion global hair color industry (which was projected to grow to $36 billion by 2027 until this news came along).

In the meantime, the Columbia study stands among many that are blaring the same message loud and clear: We are too stressed out, and it is neither optimal for employers nor employees. Another eye-opening piece of research from earlier this year found that a five-hour workday was optimal for productivity; anything longer than that, and you start to burn people out in the long run. There are trade-offs, of course; CEOs who made the switch noted a decline in the cohesion of workplace culture. But the stress caused by longer days may matter more, particularly if that workplace culture starts seeing hair color decline as a sign of burning out.

One day soon, then, perhaps your manager will inspect your head for signs of stress. More than five new gray hairs, and it's off on mandatory vacation you go. Give our regards to your melanocytes.