Stress and aging can cause hair to turn gray or white due to increased nerve fibers releasing adrenaline to the hair follicle.

“Actually the reason people go gray is because when you're really stressed, did you know this, that when you're really stressed, there's an increase in the nerve fibers that release adrenaline to the hair follicle and that activates peroxide groups in the hair follicle that cause the hair to actually go gray or white. So actually stress does make your hair gray or white. Aging does it too.”