How Our Hair Turns Gray

By Jessa Forte Netting|Sunday, May 01, 2005

Sometimes scientists need to solve one mystery before they can take on another. That’s what happened when David Fisher, a cancer researcher at Harvard Medical School, and his colleagues set out to understand melanoma, a type of skin cancer. To do it, they first had to figure out why human hair turns gray.

Fisher’s goal was to understand how to strike down the skin cells called melanocytes when they inexplicably go out of control and cause melanoma. Normally these cells manufacture melanin, the pigment that colors our hair and skin. But what does it mean when our hair turns gray? Do hair melanocytes simply stop producing these pigments? Or do they just die off?

The answer is crucial. If the hair melanocytes do die off, perhaps scientists can find a trigger that tells cancerous skin melanocytes to die as well. Skin melanocytes—whether cancerous or not—are particularly hard to kill. Their hardiness probably results from the need to resist assaults like UV radiation from sunlight. “The drawback is that the malignant form has retained this resistance,” Fisher says.

His team studied gray hair by tracking the life cycle of melanocytes in mice with genetic mutations that make their fur turn white prematurely. The team found that the stem cells that make new melanocytes were failing. After a while the stem cells died altogether, meaning that no new melanocytes would be produced. Without pigment, hair grows in white. Fisher’s team then looked at human hair follicles and found that the same process occurs in older people.

Now that the team has figured out why hair turns gray, the next step is to find ways to induce the same scenario in melanoma. “This,” says Fisher, “is essentially identifying an Achilles’ heel.”  

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