Science has proven what we’ve known anecdotally for years–stress does indeed cause premature hair-graying. A new study led by postdoctoral fellow Bing Zhang used mice to connect the dots between stress, fight or flight, stem-cell depletion, and premature graying. Hsu and her colleagues injected mice with a capsaicin-like compound, which is the active ingredient in chili peppers. The results? The rodents’ hair turned white within five days’ time. As the BBC observed, “Pain in mice triggered the release of adrenaline and cortisol, making their hearts beat faster and blood pressure rise, affecting the nervous system and causing acute stress.” So how could the scientists know what exactly was causing the rodents’ sudden Marie Antoinette syndrome? As Science News reports, “After eliminating the immune system and the stress hormone cortisol as causes of the color change, the team discovered that part of the animals’ nervous system was depleting pigment cells from hair.” Hair follicles contain pigment cells that make melanin, which determines the natural color of our hair. These pigment cells, called melanocytes, gradually die as we get older, but it turns out that stress can affect them as well. In the first scientific link between stress and hair graying, researchers from the Universities of Sao Paulo and Harvard found that “stressful events damage the stem cells that are responsible for producing pigment in hair,” according to the New York Times. Stress triggers the body’s fight-or-flight response which is driven by the sympathetic nervous system. According to livescience.com, the body quickly and involuntary responds to dangerous or stressful situations by increasing your “blood pressure, breathing rate, and hormone flow.” Sympathetic nerves branch out into each hair follicle. Stress triggers “the activation of these sympathetic nerves leads to burst release of the neurotransmitter noradrenaline” according to the study. Also known as noradrenaline, the neurotransmitter norepinephrine “causes the stem cells to activate excessively” as described by Harvard Medical School. As the BBC put it, stressing the mice out “sped up the depletion of stem cells that produced melanin in hair follicles.” In other words, pigment-producing cells plummet. No pigment cells means no color. As the New York Times explains, “Stress makes the stem cells differentiate faster, exhausting their number and resulting in strands that are more likely to be transparent — gray.” The damage is permanent. Dr. Zhang points out that “Acute stress, particularly the fight-or-flight response, has been traditionally viewed to be beneficial for an animal’s survival. But in this case, acute stress causes permanent depletion of stem cells.” As Science News says, “The body can’t replenish the stem cells, so as these cells are used up, color vanishes.” Stress leads to many reactions we can’t see, including high blood pressure, heart attacks, anxiety, and depression. But this study opens the door into how our tissues and stem cells change under stress. Someday we may be able to modify or block the damaging effects of stress. Learning more may eventually lead researches to “create treatments that can halt or reverse its detrimental impact,” Dr. Hsu said.