Hair turns gray as pigment cells stop producing melanin.
Each strand of your hair — most adults have more than 100,000 stands — is anchored to your scalp with a root. Just beneath the skin, the root is surrounded by a tube of tissue called a follicle. The follicles contain pigment cells, which produce melanin, the same chemical that make freckles or turns your skin a bronze color after a day in the sun. The amount of melanin your hair follicles produce determines whether you’re a brunette, blonde, redhead, or somewhere in between. But as you age, the pigment cells die. With fewer and fewer color boosters, your hair strands will appear gray, white, or silver. Scientists don’t know if stress — such as having children — accelerates the graying process.