Stress turns hair gray by triggering the body’s fight-or-flight response

Researchers recently reported in Nature that stress does in fact lead to graying hair, and they have identified how exactly it happens!

Stress triggers the natural fight-or-flight response in the body that we are all familiar with. This response causes the pigment-producing cells that give hair its color to decrease in number. As the cells diminish in number, the color of the subject’s hair also begins to fade away.

It’s been a common thought for a long time that stress leads to gray hair, but until now scientists couldn’t explain why.

“It was satisfying to question a popular assumption … [and] to identify the mechanisms that now open up new areas of work,” says Ya-Chieh Hsu, a stem cell biologist at Harvard University.

Hsu and her colleagues stressed mice by injecting them with a compound closely related to capsaicin, the active ingredient in chili peppers. Within five days, the rodents’ hair turned white. 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.

In hair follicles, cells called melanocyte stem cells color hair by converting into pigment-producing cells. The body can’t replenish the stem cells, so as these cells are used up, color vanishes. Sensory stress triggered a mouse’s sympathetic nervous system — which controls the body’s fight-or-flight response to stress — to release the neurotransmitter norepinephrine, the team found. That compound overactivates the reservoir of stem cells, setting off a flurry of conversion into pigment-producing cells. That, in turn, rapidly uses up the stem cells supply.

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