The breakdown of pigment-producing cells causes old people's hair to turn gray or white.
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The science of hair color, or lack thereof, isn't very well understood. Many questions remain as to why old age and extreme stress can cause hair to turn gray. Now, new research has advanced our scientific understanding of the graying process — and may be a step toward its prevention.
As detailed in the latest issue of the journal Cell, researchers have identified the chemical pathway by which hair-generating cells "ask" for hair pigment from pigment-producing cells. "The hair-generating stem cells send 'Wnt' signals to the melanocyte stem cells to activate them," Piul Rabbani, a PhD candidate in the NYU Langone Medical Center Department of Dermatology and lead author of the study, told Life's Little Mysteries, a sister site to LiveScience.
Melanocytes produce melanin, the pigment that gives skin and hair their color. When so-called Wnt proteins bind to melanocytes, this causes them to start proliferating. The melanocyte stem cells both replace themselves and generate so-called daughter cells. "It is their daughter cells that go on to produce the pigment that is incorporating into the hair," Rabbani said.
The amount of melanin those daughter cells produce — an amount defined by your genes — determines whether you're a brunette, blonde, redhead or something in between.
"With old age, however, gray hair results from defective maintenance of the melanocyte stem cells, which causes them to die or just not function as usual," Rabbani said. With fewer and fewer color boosters, your hair strands will appear gray, white or silver. What exactly causes this decay is still not understood, but Wnt signaling may have something to do with it.
It is also not known why stress or shock seem to speed along the graying process, but the new research on Wnt signaling may provide clues as to why this happens also. "Whether Wnt interacts with chemical pathways that are induced by stress and whether that affects melanocytes is an interesting question," Rabbani said.
This article was corrected on 6/17/2011 to reflect the fact that Piul Rabbani is not a dermatologist, but rather a PhD candidate in dermatology.