The vast majority of people between the ages of 45 and 65 have at least some gray hair — but what causes it? A  study  published last week in  Nature   revealed a new potential answer.

Study details

For the study, researchers from  NYU  Grossman School of Medicine looked at melanocyte stem cells (McSCs), which are the primary mechanism responsible for giving color to skin, eyes, and hair, in mice.

These stem cells reside in hair follicles and receive protein signals that stimulate them to mature into pigment-producing cells, ultimately providing hair with its color.

The researchers tracked how these stem cells moved throughout hair follicles over time.

To stimulate a hair growth cycle, they repeatedly plucked and observed the regrowth of mice hair over two years. The researchers found that the number of trapped McSCs in the hair follicle bulge increased from 15% to approximately 50%. Hairs that were not plucked and allowed McSCs to continue to move between the follicle bulge and other parts of the hair follicle were still able to generate consistent pigment.

As hairs continued to grow and shed over time, more stem cells became stuck in the follicle bulge, preventing them from getting the signal to mature and create pigment — which could then cause hair to turn gray.

What does this mean?

While the study was conducted on mice, the researchers believe their findings apply to human hair graying as well, and hope their discoveries could pave the way for preventing or reversing graying hair.

Mayumi Ito, an author of the study and a dermatology professor at NYU Grossman School of Medicine, stated the findings are a "really big step" toward understanding the graying process, and challenge the belief that gray hair results solely from the exhaustion of the pool of melanocyte stem cells.

While these findings provide a clearer picture of gray hair's cellular causes, Jenna Lester, a dermatologist and professor at the University of California, San Francisco, explained that a variety of factors, including sun exposure, hormones, stress, genetics, and certain medical conditions, can influence hair color longevity.

But the new study could offer hope for those seeking to prevent or reverse gray hair. Researchers believe that relocating trapped McSCs to the correct position could slow the graying process.
Melissa Harris, a biologist at the  University of Alabama at Birmingham  who was not involved with the study, noted the potential insights into stem cell behavior from the study could also aid researchers in other fields.

"I think sometimes people take the hair for granted," she said, "but in a sense, it makes it actually really easy for us to see potential ways in which aging or other perturbations affect our bodies." (Martin, USA Today, 4/20; Olson, NPR, 4/21; Golembiewski, New York Times, 4/19)