Gray hair could play surprising role in cancer defense, study suggests

Why does hair turn gray? And how is that common hallmark of aging connected to a life-threatening disease? 

A new study may have pinpointed how going gray is connected to one of the deadliest forms of skin cancer.

Researchers at Tokyo Medical and Dental University, led by Dr. Emi K. Nishimura, found that pigment-producing stem cells in hair follicles respond to stress in dramatically different ways.

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Depending on their environment, those cells can either die off, which leads to gray hair, or survive and multiply in ways that could trigger melanoma, according to a university press release.

The findings were published Oct. 6 in the journal Nature Cell Biology.

The team studied melanocyte stem cells, the cells that give hair and skin their color, using mouse models and tissue samples. In exposing these cells to forms of stress that damage DNA — such as chemicals that mimic UV exposure — the scientists observed how the cells behaved inside their natural setting.

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Some of the cells responded to the damage by stopping their normal self-renewal process and turning into mature pigment cells that soon died. This left the hair without its source of color, producing graying.

But when the researchers altered the surrounding tissue to encourage cell survival, the damaged stem cells began dividing again instead of shutting down. Those surviving cells accumulated more genetic damage, and, in some cases, started behaving like cancer cells.

Additional experiments showed that certain signals from the cells’ environment — including one molecule called KIT ligand, which promotes cell growth — helped determine which way the cells went, the release stated.

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In other words, the same kind of cell could either fade out harmlessly or become the seed of melanoma, depending on the cues it received from nearby tissue.

“It reframes hair graying and melanoma not as unrelated events, but as divergent outcomes of stem cell stress responses,” Nishimura said in the release.

Nishimura’s team described the process as a biological trade-off between aging and cancer, but that doesn’t mean gray hair prevents cancer.

“It reframes hair graying and melanoma not as unrelated events, but as divergent outcomes of stem cell stress responses.”

Instead, it shows that when pigment cells stop dividing and die off, it’s the body’s way of getting rid of damaged cells, the researchers noted. If that process doesn’t happen and the damaged cells stick around, they could turn into cancer.

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The study was conducted in mice, but its implications could help scientists understand why some people develop melanoma without obvious warning signs, and how the natural mechanisms of aging could actually protect against cancer.

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For now, the researchers say the discovery shows how finely balanced the body’s cellular responses are and how small changes in that balance can mean the difference between a harmless sign of aging and a life-threatening disease.