Stress turns hair gray.

Where did you get your grays? You probably think of a rebellious child, a job that kept you up at night or a parent in failing health. In other words, you think of stress.

Turns out, you’re not far off. This study showed that genotoxic stressors, meaning any substances (internal or external) that can damage DNA, speed up the aging process by turning hair prematurely gray.

Let’s break it down: Your hair contains melanocyte stem cells in the hair follicle. Normally, as a new hair grows, some of those stem cells mature into melanocytes (melanin-producing cells that give your hair color). The remaining stem cells renew constantly so that your hair can keep producing color.

Under stress, that process goes haywire.

Researchers exposed mice to x-rays and chemotherapy (both genotoxic stressors), and found that the damaged melanocyte stem cells matured too early, leaving a smaller store of stem cells. As a result, the mice couldn’t produce enough melanocytes, or pigment-producing cells, and new strands were starved for color—hello, grays.

What does this mean for you? The stressed mice’s hair follicles actually mirrored elderly mice, suggesting that genotoxic stressors found in our environment (like the sun’s rays, household chemicals, and pollution) may drive natural graying.

If you want to keep that natural color, de-stress your tresses.

Summer hits and the sun’s rays give your hair sexy, “natural” highlights. But what’s the hidden cost? Scientifically speaking, those highlights are UV damage to the pigment-producing cells in your hair. Usually our color returns, but as we age, our bodies are less able to repair the damaged cells.

We’re not suggesting you stay inside all summer, but if you want to keep that pigment as long as possible, try sporting a wide-rimmed sun hat—you know, Derby-style.