New study may explain for the first time why we get gray hair

Science has long known that the pigment melanin is responsible for the color of our hair. It was also known that we turn gray when certain pigment-producing cells – the so-called melanocytes – are no longer sufficiently available. When and why this circumstance plays a role, however, was not known until now – just as little as how and whether it could be prevented.

A new study has now made progress in this regard. The study by the research group at New York University’s Grossman School of Medicine may also call into question previous theories about melanocyte development.

Like other cells, melanocytes arise from stem cells. The melanocyte stem cells reside in the hair follicle and it is these stem cells that are the focus of the latest research. However, in their study, the researchers noticed that the behavior of melanocyte stem cells differs from that of other stem cells.

To learn more about the behavior of stem cells in the different phases of hair growth, the researchers tracked and imaged individual cells in the fur of mice for two years. To her surprise, the stem cells migrated back and forth in the hair follicle, going in and out of their more mature, pigment-producing state.

“We were surprised,” said Dr Zon, one of the researchers. The observation that a group of stem cells alternate between adult and young does not fit with previous explanations for why hair turns gray.

What the researchers realized was that this change in the cells’ state depended on exactly where the stem cells are located in the hair follicle: they are only influenced by signals from proteins that promote maturation in certain locations.

Now it turned out that these precursors – the stem cells – of the pigment-producing cells become trapped as the hair ages. And in a region the researchers call the “follicle bulge.” Because they do not receive growth signals from proteins at this site, the stem cells no longer develop in sufficient numbers into melanocytes, which in turn should fill the growing hair strand with color.

In experiments on mice, the researchers forced an artificial aging process by pulling out hair. The result: The number of hair follicles containing melanocyte stem cells that got trapped in this bulge rose from 15 percent to almost half.

Of course, the findings have yet to be observed in human hair follicles – but it seems quite possible that the same mechanisms are happening in our own hair as well. In the long run, these outcrops could even provide a way to treat hair to keep it from losing its color.

“Our study adds to our fundamental understanding of how melanocyte stem cells work in hair coloring,” said study leader Qi Sun. “The newly discovered mechanisms suggest that the same fixed positioning of melanocyte stem cells also exists in humans.” If so, it’s a possible way to reverse — or prevent — human hair graying by getting clogged cells moving again.

However, it is worth noting that other mechanisms are also at play here – the graying of our hair is not only due to the melanocyte stem cells. It is known from previous studies that genetics and stress levels also play a role in hair aging.