Grey hair might reflect a hidden defence that clears damaged cells and lowers melanoma risk, says study
When you spot a silver strand in the mirror, you normally chalk it up to getting older. But scientists at the University of Tokyo say that strand might signal something far more interesting: a built-in defence mechanism in your skin and hair. Their work shows that in mice, stem cells responsible for hair pigmentation either surrender and go grey or bypass the exit strategy and stay around with damage that could lead to cancer.
The process hinges on what happens when the melanocyte stem cells (McSCs) that live in hair follicles suffer DNA damage. According to the study published in Nature Cell Biology on October 6, 2025, if these cells trigger a protective programme, they mature, leave the stem-cell niche, and the hair turns grey. That programme is called “seno-differentiation.”
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Potential damage and how hair greys
Here is how it works. Under standard genotoxic stress, these stem cells hit a checkpoint and stop renewing themselves. Then they differentiate into pigment cells one last time, exit the hair-follicle stem zone and get cleared out. The follicles lose their pigment factory, and the hair goes grey. This looks like a cost, but the trade-off is that potentially dangerous, damaged stem cells no longer hang around.
When the damage comes via carcinogens (like UVB or DMBA), the protective switch seems blocked. The environment around the stem cells pumps out more KIT ligand (KITL) and other signals. Those boost survival and suppress the “exit” route. The damaged stem cells stick around, replicate and even expand, raising melanoma risk.
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What it could mean for ageing, hair and cancer risk
This work does not mean grey hair is equal to cancer immunity. The researchers stress that greying is not a guarantee of protection, but it can mark where the body has cleared a dangerous cell. As the press release puts it: “This study does not suggest that greying hair prevents cancer, but rather that seno-differentiation represents a stress-induced protective pathway that removes potentially harmful cells.”
For ageing skin or sun-exposed regions such as temples and crown, early or increased greying may hint at a more active elimination of damaged stem cells. The flip side: fewer stem cell reserves might accelerate visible ageing. But visible ageing might conceal a hidden protective strategy, resulting in a strange paradox.
Looking ahead, could treatments that reverse or prevent grey hair inadvertently keep damaged stem cells alive? The question remains. The research opens up fresh thinking: ageing and cancer risk are not just about damage accumulation – they are about how your body chooses to deal with damage.
Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.
