WEDNESDAY, April 19, 2023 (HealthDay News) -- Folks develop gray hair as they age because color-producing stem cells become “stuck” and disabled in the hair follicle, new animal research contends.

Hair color is controlled by melanocyte stem cells (McSCs), which as they mature produce the protein pigments that turn people into brunettes, blondes and redheads.

During normal hair growth, these cells are continually on the move, transitioning back and forth between different growth compartments in the follicle, researchers noted.

This ability to move back and forth is unique to the color-producing stem cells, they said.

For example, the stem cells that create the hair follicle itself are known to move in only one direction along an established timeline as they mature. This helps explain in part why hair can keep growing even while its pigmentation fails and it goes gray.

But increasing numbers of these stem cells get stuck in a middle part of the hair follicle called the “bulge” as hair ages, sheds and then repeatedly grows back, the researchers discovered.

Stem cells stuck in the hair follicle bulge aren’t able to properly mature or get the necessary signals from the body to produce pigment, the research team reports in the journal Nature.

In this experiment, researchers physically aged the hair of mice through plucking and forced regrowth.

As a result, the number of hair follicles with McSCs lodged in the follicle bulge increased from 15% before plucking to nearly half after forced aging.

Those stuck cells remained incapable of regenerating or maturing into pigment-producing melanocytes, researchers found. The cells couldn’t regenerate or produce pigment in new hair follicles because they didn’t receive the necessary signals from the body.

By contrast, other McSCs continued to move back and forth between the follicle bulge and the hair germ, a lower part of the follicle from which new hairs form. Those cells retained their ability to regenerate, mature and produce pigment over the two-year study period.

“It is the loss of chameleon-like function in melanocyte stem cells that may be responsible for graying and loss of hair color,” said study co-author Mayumi Ito, a professor in the departments of dermatology and cell biology at NYU Langone Health.

If that’s true, keeping hair healthy and colored would involve figuring out a way to free these stuck cells, Ito said in a Langone news release.

Results of animal studies don't always apply to humans. Still, "our study adds to our basic understanding of how melanocyte stem cells work to color hair,” said study co-author Qi Sun, a postdoctoral fellow at NYU Langone Health.

“The newfound mechanisms raise the possibility that the same fixed-positioning of melanocyte stem cells may exist in humans. If so, it presents a potential pathway for reversing or preventing the graying of human hair by helping jammed cells to move again between developing hair follicle compartments,” Sun said in the release.

More information

The Cleveland Clinic has more about hair follicles.

SOURCE: NYU Langone Health, news release, April 19, 2023