The color of our hair is created by the pigment-producing cells, called melanocytes, located in each hair follicle. In the process of generating the pigment for our hair, these cells also produce some other chemicals, one of which is hydrogen peroxide (yes, the stuff that bleaches your hair). When we’re young, our bodies also produce enzymes to neutralize that hydrogen peroxide and other free radicals so our hair keeps growing in with color. As we age, however, those neutralizing enzymes become less active than they once were, which means that hydrogen peroxide starts to build up and sap color from our hair, leaving it a lovely shade of gray—and, eventually, white, once the strand has lost all its pigment.
Although most gray is related to a natural part of the aging process, a significant environmental factor is UV exposure, which can accelerate hair aging. One study—on mice, not humans—demonstrated that not only did UV exposure produce gray hairs, but it also decreased the diameter of the hairs and shortened the shafts of the roots. To be more specific, exposure to UVA rays (those longer wavelengths) damages hair pigment, while UVB exposure (shorter wavelengths) damages hair proteins, specifically keratin. So sunlight, which carries both UVA and UVB, is a double-whammy for hair damage.
In addition to UV exposure, other lifestyle factors contribute to going gray, like smoking, anemia, poor nutrition, low B vitamins, and untreated thyroid conditions, says Hadley King, MD, a dermatologist based in New York City. Genetics can also play a role; if your parents went gray at a younger age, you probably will too.
One contributing factor that might be a bit more in our control is stress. Scientists found that the body’s “fight or flight” response can contribute to turning hair gray. Remember those pigment-producing cells, the melanocytes? When you’re under stress, you release a hormone called norepinephrine, which basically causes your body to go into overdrive—and burn through stem cells at a much faster rate. This means that, as your hair’s pigment-producing melanocytes die off (they typically live about 3 to 5 years), there aren’t enough active stem cells to replace them all… and some hair starts to grow in without pigment, i.e. turn gray.
Is reversing gray hair possible?
Maybe, especially if you’ve just discovered your first strands of silver. “We know that during periods of stress, individual hairs on your head can go gray. And then they’ll turn back once the stressor is removed,” says James O’Sullivan, Ph.D., a postdoctoral research associate in developmental biology and cell metabolism, who has been involved in research on the topic.