By Song Hye-jin | THE CHOSUNILBO A study has found that gray hair may not only be a sign of aging but also a trace of the body’s process of blocking cancer cells on its own. The research team from the University of Tokyo’s Institute of Medical Science discovered a link between graying hair and the body’s cancer defense mechanism and published their findings this month in the international journal "Nature Cell Biology." The team began studying melanocyte stem cells (McSC) while seeking answers to the question, “Why do some stem cells die or disappear when their DNA is damaged, while others survive and transform into cancer cells?” These cells periodically regenerate to produce melanin pigment. The researchers exposed lab mice to intense ultraviolet rays and chemicals to damage the DNA of McSC cells, then observed the cellular response. Some McSC cells recognized themselves as “cancer-risk cells,” stopped self-regenerating, and died. This process turned the mice’s fur white, as the dying McSC cells no longer produced melanin. In contrast, some cells continued self-replicating even after DNA damage, accumulating genetic mutations and transforming into melanoma. These were cells that increased cancer risk. The team also identified the molecular signal that induces McSC cells to self-destruct, causing gray hair. This is the DNA damage defense system called the “p53–p21 pathway.” If this signal is weak or inactive, the likelihood of cancer cell proliferation increases. The researchers stated, “Hair turning white may not simply be an aging phenomenon but a biological defense response that blocks the path to cancer by eliminating damaged cells.”