It’s not an old wives’ tale. Stress really can turn your hair white. Sometimes referred to as the Marie Antoinette syndrome, it can even happen overnight from a severe fright.

People have accepted the idea for a long time. Millions of teenagers have been accused of causing their parents’ gray hairs. But scientists weren’t so sure.  Parents tend to reach the age where the first gray hairs typically emerge, so the presence—and stress—of teenagers in the house may be pure coincidence.  Aging is still the most common reason we turn gray.

Then, in 2016, researchers confirmed that stress could be directly responsible for gray hairs. But how that happened was still unclear. For the next few years, a group at Harvard tested several hypotheses.  

One of the most likely links they suspected was the hormone cortisol. Your adrenal glands flood your body with this steroid to protect you when you are under stress. It affects glucose metabolism in your bloodstream, blood pressure, and blood circulation to prepare you for survival under duress.

That proved to be a blind alley.

Certain illnesses and nutritional deficiencies can also bring on the gray. That type of grayness may be reversible.  The usual culprits are low vitamin B12, iron and high-density cholesterol. But those aren’t factors in sudden graying from stress. And you can even reverse the graying process from these processes if the deficiencies are treated.

In contrast, when stress is the reason for hair to go gray, the condition is permanent.

Finally, in a paper just published this year in Nature, Harvard researchers unveiled the “root” of the problem.  Literally the root of your hairs, or follicles. The follicle is the tiny sac from which each hair grows. That’s where the stem cells that supply melanin live. These stem cells convert into pigment-producing cells that give your hair color. When stress injures or destroys them, they are no longer able to produce melanin, and new hairs emerge as gray or white. 

Now that we know what is happening, the question is how to use it. So far, there is no magic to restore pigment stem cells in your scalp.

The one thing this research does tell you, however, is that stress is serious business. It affects your body in numerous ways. Gray hair is cosmetic. Other side effects of uncontrolled stress like heart attacks and strokes are much more frightening.

Whatever you need to do to deal with excess stress—whether it’s exercise, yoga, meditation, changing jobs, saying no to overwhelming obligations, or medical help, do it. Don’t give stress the upper hand because it could bring you down.