That’s democratic, not fair. When men go gray, of course, they are sometimes praised for their silvery manes – even if the closest they have ever come to a veld was watching “Born Free.” If there is a comparably laudatory descriptive for women, it does not immediately come to mind.



But let’s go back to that idea of hair “going gray,” because it’s a bit of a misnomer. As baby boomers watch their locks turn gray, the only thing going anywhere is a pigment called melanin, which gives hair its color.



The cells that make up melanin can be found in the skin’s follicles, the tiny sacs under the skin that produce hair. As hairs form, they get an infusion of the pigment. Melanin comes in two flavors: light and dark. How much goes into a strand of hair, and in what mix, determines its color.



Sooner or later, even as your hair keeps growing, those little pots of ink in the follicles start running dry. O.K.: there aren’t really little pots. And there isn’t an allotted amount of pigment. But at some point, the production of melanin slows. Dr. Amy Derick, a clinical instructor of dermatology at Northwestern, says that the exact mechanism is unknown, but that reports have shown that pigment-producing melanocyte stem cells undergo programmed cell death, a process called apoptosis.



Some scientists also believe that an accumulation of hydrogen peroxide — which, it turns out, is produced naturally in the hair; why have bottle blondes been going to the drugstore all this time? — blocks production of melanin.



When this happens, it is at least in part a matter of genetics, though some medical conditions can affect hair color. Think of it as the 50-50-50 rule: if you are 50, there’s a 50 percent chance that 50 percent of your hair is gray, as our colleagues at the Well blog have noted. After age 30, some researchers have found, your chance of going gray rises 10 percent to 20 percent each decade.



Whatever the case, as the pigment’s presence dwindles, hair turns first gray and then white — or silver, if you are running for office.



Questions on aging? E-mail boomerwhy@nytimes.com.