Why does our hair turn gray—as opposed to green or some other color—as we age?

Why does our hair turn gray—as opposed to green or some other color—as we age?
Gray hair, sagging skin, wrinkles—all signs of aging can be traced to the same cause: dying cells…

Gray hair, sagging skin, wrinkles—all these signs of aging can be traced to the same cause—dying cells, said MIT biologist Lenny Guarente, author of the 2007 book Ageless Quest.

Hair follicle cells cooperate with cells that produce pigments such as melanin that make hair shades of brown, black, blond or red, said Guarente, a pioneer and leader in the study of the molecular biology of aging. As we get older, the pigment-producing cells fail, and the only thing left is the white, unpigmented protein that makes up the hair shaft.

“The reason we lose the ability to make the pigments is that we lose a lot of cells as we get older,” he said, including the subcutaneous fat cells that keep skin looking smooth and wrinkle-free. “Those cells die with age. A lot of the physical aspects of aging can be explained by damage to important macro-molecules and death of cells.”

Guarente’s lab studies sirtuins—proteins that are now understood to retard aging in a wide variety of organisms. While he is interested in reversing symptoms of age-related diseases, not improving appearance, he expects that his work, which “attacks the aging process high up in the heierarchy” may affect a lot of things in the mix—including, potentially, graying hair. At MIT, one-third of the engineers now work on biological problems, including cancer research. – Deborah Halber

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December 18, 2008