Why does stress cause gray hair?

We don't yet know: According to scientific american, "scientists are beginning to gather clues that stress can hasten the graying process, but there is no scientific evidence demonstrating a cause-and-effect relationship." the possible explanations are technical and have to do with the effects of stress hormones interfering with the delivery of pigment to the hair. Genetic programing certainly plays a big role.

Graying of hair is: Related to genetic predisposition. The age of initial graying is largely a matter of genetics. However stressors such as nutritional deficiencies, traumatic head injuries, low vitamin b levels, zinc deficiency, severe illness, surgery and marked emotional stress may impact earlier depigmentation in people who are already predisposed to gray hair. In general – genetics plays the biggest role.