Almost everyone has heard the old saying about stress causing gray hair. Now, scientists have found evidence that is true. But they also have some good news: Stress-induced gray hair is reversible.

To establish their findings, the Columbia University scientists were literally splitting hairs. The developed a new way to capture detailed images of tiny slices of human hairs in order to document growth patterns.

Like rings on a tree trunk, hair growth can reveal much about our biological history. While embedded in the skin as follicles, hairs are influenced by stress hormones. As the hair grows longer, those changes — including shades of gray — are hardened and preserved.

Using a high-resolution scanner, that’s what the researchers capitalized on. Hair from a group of volunteers was cataloged, along with a corresponding diary that documented the participants’ stress levels. Using a mathematical model, they determined that stress-induced changes in the part of a cell known as the mitochondria may explain how stress makes hair gray.

More broadly, what emerged was an association between stress and hair color. As stress subsided, so did some gray in the hair. In one case, a study participant went on vacation. When they did, five hairs reverted from gray to its original, dark color — right in sync with the vacation.

Yet the researchers also not that reducing stress won’t return hair to its original color all by itself. Stress may actually just be the last straw, pushing hair that is already on the edge of turning gray due to age and other factors.

So if hair coloring isn’t your thing, try keeping a lid your stress. It may help keep the gray away.