Can a Person’s Hair Turn White Overnight?
The stories you may have heard of people whose hair turned white overnight, due to shock or fright, are not true. Hair color comes from melanin, a pigment deposited in the hair cells as they form in the root. As people grow older, pigment is no longer deposited in the newly forming hair cells. The hair gradually becomes gray or white.
Certain diseases, as well as worry or shock, can cause the body to stop or slow down the production of melanin. It can be exacerbated by stress, which could account for the association of white hair with terrifying experiences. Men and women under stress have been known to become white-haired in just a few months.
The medical name for the sudden whitening of the hair is canities subita. The best explanation for it is not that the hair changes color, but that the pigmented hairs fall out. It is thought to be caused by an auto-immune response, where the body’s defence system turns on itself.
A severe shock could trigger hair loss, but with only the colored hairs falling out, leaving someone who already has some grays with a whole head of white hair. Or perhaps the immune response might target the pigment-producing system, which would explain why those no follicles no longer producing colored hair are unaffected.
The puzzle of whether your hair can turn gray sounds like a simple one for medical science to solve, but it’s not. Ultimately, to study exactly what happens you would need to examine the hair before and after a shocking incident, carefully assessing its color and thickness. Life-threatening situations are not only rare, but unpredictable and no ethics committee is going to let you induce a sufficiently terrifying experience in a lab volunteer.