Researchers at the University of Tokyo have discovered that the same process that causes hair to turn gray may also protect the body from developing skin cancer.
The study, published on October 6, 2025, in Nature Cell Biology, found that pigment-producing stem cells in hair follicles called melanocyte stem cells (McSCs)—react to DNA damage in two different ways. These reactions can either lead to gray hair or, in other circumstances, to melanoma, a dangerous form of skin cancer.
Throughout life, our cells are constantly exposed to stress from sunlight, chemicals, and internal changes that damage DNA. Such damage can cause both aging and cancer, but scientists have not fully understood how stem cells decide whether to protect or harm the body—until now.
Professor Emi Nishimura and Assistant Professor Yasuaki Mohri led the research team. Using long-term experiments in mice, they tracked how melanocyte stem cells respond when their DNA is damaged.
They found that when these cells detect serious DNA breaks, they enter a process called senescence-coupled differentiation or seno-differentiation. This means the cells stop dividing and mature into pigment cells that are eventually lost, resulting in gray hair.This, the researchers say, is the body’s way of protecting itself.
However, when these stem cells are exposed to certain carcinogens such as ultraviolet (UV) rays or a chemical called 7,12-dimethylbenz(a)anthracene they sometimes skip this protective step. Instead, they keep dividing and growing, even with DNA damage. This uncontrolled growth, supported by a molecule called KIT ligand, can lead to the development of melanoma.
Professor Nishimura explained, “The same stem cells can either stop functioning or start multiplying, depending on the type of stress they experience and the signals around them. This means that graying hair and melanoma are two sides of the same coin.”
The researchers emphasize that gray hair doesn’t mean you’re safe from cancer, but the graying process itself might reflect a built-in defense mechanism a way for the body to get rid of cells that could otherwise become harmful.
Their findings offer a new way to understand how aging and cancer are connected and suggest that losing pigment cells through graying could be part of the body’s natural strategy to stay healthy.
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