Scientists have studied the phenomena for decades, but the science behind what causes hair to turn gray is still murky. Most scientists agree that genetics and heredity play a major role in determining when we go gray. And while there has been no proven link, some scientists believe that stress may also contribute to premature gray hair.
Hair color is produced from a pigment called melanin, which is manufactured by the melanocyte stem cells in our hair follicles. Unlike neighboring keratinocyte stem cells, which build hair, melanoctye stem cells have shorter life spans and begin to die off when most of us are in our 30s. Lose enough melanin, and your hair turns gray. Hair that has lost all of its melanin is white.
A 2009 study published in The FASEB Journal suggests another possible cause for graying hair: hydrogen peroxide. While our hair follicles create a small amount of the bleaching agent naturally, the chemical begins to build up over time and ends up blocking melanocyte stem cells from producing melanin. Basically, our hair bleaches itself from the inside out.
As of yet, there is no clear link between gray hair and stress. The study published in The FASEB Journal suggests that stress and the wear and tear of our hair follicles can lower catalase, an enzyme that breaks down hydrogen peroxide into water and oxygen, producing more hydrogen peroxide. Other scientists theorize that stress hormones like cortisol produce unstable molecules called free radicals, which may damage the melanocyte stem cells and affect the melanin.
Scientists tend to agree that the main factor involved in gray hair is genetics. Whether it is caused by a single gene or a cluster of genes is unknown, but you will most likely go gray around the same age as your parents or grandparents did. Interestingly, what scientists haven’t found is a link between premature graying and premature aging, meaning that people who gray early don’t die any earlier than people who gray later.
A variety of other factors can contribute to gray hair. Poor nutrition, B12 deficiencies, lack of iron in the blood (anemia), and thyroid problems have been known to lead to premature graying. Smoking, which saps the oxygen in body tissue, may also play a role in graying hair.
Contrary to urban legend, a major shock or trauma will not turn a person’s hair gray overnight. This myth most likely stemmed from a rare disease known as “diffuse alopecia areata,” which causes the pigmented hairs to stop growing, leaving only the white and gray hairs behind.