You’re a smoker

“Smoking is of the worst things you can do for your skin and hair,” says Dr. Jihn. In fact, research has shown an association between cigarette smoking and the onset of gray hair before age 30. “If you look at smokers, you can see the wrinkles in their skin,” she says. “You may not be able to see wrinkles on the scalp, but it’s still affecting all the follicles.”

All that said, Dr. Jihn still emphasizes that all of these factors have much less of an impact on your hair color than your genes. “But if you notice you’re getting premature graying and it doesn’t run in your family,” says Dr. Jihn, “then you should see your doctor to check if your thyroid is okay, your vitamin levels are fine, and that you don’t have anemia.”

This article originally appeared on Health.com