Why Does Hair Turn Gray?

salt and pepper hair, silver, gray, white hair, aging, melanin
Hair turns gray as pigment cells stop producing melanin. (Image credit: Dreamstime)

As people age, they are confronted with the prospect of life with gray hair. But why does hair turn gray?

Each strand of your hair — most adults have more than 100,000 strands — 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.

Hair turns gray due to a natural buildup of hydrogen peroxide in hair follicles, which causes oxidative stress and graying. 

In younger people, an enzyme called catalase breaks down hydrogen peroxide into water and oxygen. But lower levels of this enzyme, combined with lower levels of enzymes called MSR A and B that repair hydrogen-peroxide damage, cause hair to turn gray as people age.

Though gray hair isn't always a welcome sign of aging, some evidence suggests it can be an indicator of good health.

Researchers in 2012 found that wild boars with significant graying hair "were actually those in prime condition and with the lowest levels of oxidative damage," researcher Ismael Galván of the Museo Nacional de Ciencias Naturales in Spain said in a statement.

"Far from being a sign of age-related decline, hair graying seems to indicate good condition in wild boars," Galván said.

And despite what your parents may have told you, scientists don’t know if stress — such as having children — accelerates the graying process.

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