Stupid Question ™
June 28, 2001
By John Ruch
Q: What makes hair turn gray? Does it start out gray in the head and then grow out, or does the whole hair turn gray at once?
A: Hairs grow out of deep pockets in the skin called follicles. Deep down in the follicle, living cells produce proteins similar to those in fingernails. As these cells multiply, they start sticking together and die, creating a shaft of hard, lifeless cells that is gradually pushed up and out of the follicle by the living cells at the bottom. This dead shaft is a hair.
Keratin, the protein that composes the hair, is itself colorless, so the fundamental color of hair is white.
However, also deep in the follicle are cells containing the pigment melanin. Kertainocytes—the hair-producing cells—actually “pinch off” a piece of the melanin-containing cells and swallow it up, according to University of Arkansas for Medical Science dermatology chief Tom Horn. As the hair cells die and harden, the melanin they’ve picked up concentrates, creating the hair color.
Hair will continue “growing” outward until it reaches an apparently genetically predetermined length, and/or falls out. The typical strand of head hair falls out after two to four years, and a new one starts forming.
Hair starts graying when the melanocytes—the melanin-producing cells—start dying. The cell death appears to be genetically determined, though the evolutionary function, if any, is unknown.
As the melanocytes age, they may actually become hyperactive, making hair considerably darker before it goes gray. Then the melanocytes typically go on the fritz, producing melanin only irregularly. Some parts of the hair will have melanin, others will have only air spaces or clear dead cells. This blend produces a gray coloration.
Eventually, the melanocytes may all die, leaving the hair pure white.
The graying occurs in the follicle and becomes visible only as the hair grows outward. The hair itself is dead matter, and its color can be changed only by external means such as bleaching, sunlight or dyes. There’s strong anecdotal evidence that severe stress can cause premature graying, though stories of people going gray overnight are incredible.
The amount of melanin in the hair varies between ethnic groups and individuals. So does the timetable for graying. In white people, graying after age 20 is considered normal. In black people, after age 30 is normal. Not all people go completely gray; those who do usually take 10 to 20 years to do so.
Premature graying is called “canities” and can be perfectly normal. However, it can also be a symptom of a variety of medical disorders. These include thyroid conditions, anemia, B12 deficiency and a rare immune disorder. Children with graying hair should always be examined by a doctor.
Much is still unknown about the graying process. Unfortunately, most of the experts work for the “gray-curing” industry and blend research with sales pitches. While synthetic hormones or gene therapy might one day “cure” graying, the process is today irreversible. The only options are to enjoy it or dye it.