Study details and key findings

For the study, researchers from the University of Tokyo examined how melanocyte stem cells (McSCs) respond to different types of DNA damage. McSCs are specialized cells that produce melanocytes, which give hair and skin their color.

Using long-term lineage tracing and gene expression profiling in mice, the researchers found that when McSCs experience DNA double-strand breaks, they undergo a process called senescence-coupled differentiation or seno-differentiation. In this state, the stem cells will permanently mature and die off, which then leads to hair turning gray.

In additional experiments, the researchers found that certain signals from the cells' environment helped determine which pathway they followed. One molecule called KIT ligand suppressed seno-differentiation and helped promote cell growth, which pushed McSCs to a more cancer-prone state.

Commentary

According to Emi Nishimura, a professor at the University of Tokyo and one of the study's authors, the study findings "reveal that the same stem cell population can follow antagonistic fates — exhaustion or expansion — depending on the type of stress and microenvironmental signals."

While seno-differentiation can help protect tissue by eliminating damaged cells and turning hair gray, exposure to carcinogens will suppress this process, leading damaged cells to continue dividing and increasing the risk of cancer within the tissue.

"Hair graying may be a sign that McSCs exceeding a certain threshold have been eliminated, protecting the skin from cancer risk," said Yasuaki Mohri, an assistant professor at the University of Tokyo and the study's lead author. "… While gray hair develops, the risk of melanoma simultaneously decreases."

Other health experts say that people should be careful about their risk of developing melanoma regardless of whether they have gray hair. Aging is also linked to developing gray hair, and the risk of melanoma increases with age. The average age of patients diagnosed with melanoma is 66, though it is also one of the most common types of cancer in people under 30.

"I would not use gray hair to predict a higher or lower risk of melanoma," said Ife Rodney, founding director of Eternal Dermatology + Aesthetics. "There are a lot of other variables that can lead to skin cancers." A history of sunburn, chronic sun exposure, a family history of skin cancer, and having light skin, hair, and eyes are all linked to an increased risk of skin cancer.

To protect yourself against skin cancer, Rodney recommends using sunscreen daily. "Strict sun protection is key," she said. "[The study] can be informative, but having gray hair should not be used to try to predict your melanoma risk or alter your behavior. You still need to practice sun protection."