From Scientific American:
Legend has it that Marie Antoinette’s hair turned white the night before she was guillotined. Presumably the stress of impending decapitation caused her locks to lose color within hours. Extremely unlikely, scientists say, but stress may play a role in a more gradual graying process. The first silvery strands usually pop up around age 30 for men and age 35 for women, but graying can begin as early as high school for some and as late as the 50s for others.
Graying begins inside the sunken pits in the scalp called follicles. A typical human head has about 100,000 of these teardrop-shaped cavities, each capable of sprouting several hairs in a lifetime. At the bottom of each follicle is a hair-growing factory where cells work together to assemble colored hair. Keratinocytes (epidermal cells) build the hair from the bottom up, stacking atop one another and eventually dying, leaving behind mostly keratin, a colorless protein that gives hair its texture and strength. (Keratin is also a primary component of nails, the outer layer of skin, animal hooves and claws?even rhinoceros horns.)
Does stress accelerate this demise of the melanocyte population?