TOKYO -- An increase in gray hair may be the result of a self-cleansing mechanism that removes damaged cells -- potentially serving as a defense against cancer, according to a study by a team of scientists from a Japanese institute.

The findings by stem cell biology professor Emi Nishimura of the University of Tokyo's Institute of Medical Science and others were published online in the British scientific journal "Nature Cell Biology," and are seen as a key insight into how melanoma -- a type of skin cancer -- develops.

Gray hair is a well-known sign of aging caused by the depletion of cells called melanocyte stem cells, which give rise to pigment-producing cells in hair follicles.

In the team's experiments, mice whose skin was artificially aged through radiation exposure developed gray hair. The researchers claim that this was a result of damaged melanocyte stem cells being depleted and expelled from the hair follicles.

In contrast, when mice were treated with carcinogenic substances, compounds that activate melanocyte stem cells were produced in their hair follicles, suppressing signs of aging. Because cell replication was promoted, damaged cells were not eliminated and remained in the follicles -- preventing graying. However, these damaged cells later transformed into melanoma.

Based on these results, the researchers concluded that graying is a process by which the body removes cells that may pose a cancer risk. Carcinogens, on the other hand, suppress this protective mechanism, sharply increasing the likelihood of cancer.

"Gray hair doesn't appear for no reason -- it reflects a selective process in which damaged cells are being eliminated," Nishimura said. "It's important for cells to age properly and be removed when necessary. People should be cautious about cosmetic procedures or topical agents without solid scientific evidence or safety validation as they may pose health risks."

(Japanese original by Yurika Tarumi, Lifestyle, Science & Environment News Department)