We finally know why stress turns your hair white

A recent paper, published Wednesday in the journal Nature, may put some of these arguments to rest. In the study, stem cell and regenerative biologists from the United States and Brazil reported that stress can indeed cause hair to lose its pigment—and they identified a cellular pathway by which it can occur.
To study this vexing relationship, the researchers created an elaborate animal model, which basically involved trying to turn black-haired rats white with lab-made stressors. They tried three different tactics: restraint stress, chronic unpredictable stress, and nociception-induced stress, which is caused by physical pain (or the threat of it). Each successfully turned the rat’s hair white. Perhaps unsurprisingly, nociception-induced stress, which the scientists stimulated by injecting the rats with resiniferatoxin, an analogue of the chili pepper compound capsaicin, worked best and fastest.