Gray Hair Isn’t Inevitable: A New Clue From Stem Cells That Get Stuck

Gray hair has long been a sign of the natural aging process. But recent research suggests there might be a way to prevent it one day. Scientists have discovered the mechanism for graying hair, which occurs when cells in the hair follicle become trapped and nonfunctional as a person ages.

How does hair get its color

The cells that colour the hair are called melanocytes. These cells make the pigment that gives a person’s hair brown, black, blond or red. Melanocytes are generated from melanocyte stem cells (McSCs).

McSCs are not unlike other stem cells – they have the ability to differentiate into specialized cells, and these cells can become melanocytes, the cells that produce hair pigment. McSCs are located in the hair follicle, the structure at the base of the hair where growth begins.

As a person’s hair begins to grow, McSCs get signals to specialize and become melanocytes, which provide growing hair with its natural color.

What makes McSCs unique is their ability to move between two compartments within the hair follicle: the hair germ and the hair follicle bulge. The cells shuttle between these two areas to pick up different signals that tell them when to specialize.

This movement matters because the two compartments carry very different levels of a signaling protein called WNT — in fact, McSCs in the bulge are exposed to trillions of times less WNT signaling than McSCs in the hair germ compartment just below it. It’s this WNT exposure that prompts the cells to mature.

The Problem With Aging Stem Cells

When a person ages, McSCs start to become dysfunctional. According to a study led by Dr. Mayumi Ito of NYU Langone Health, as people age, melanocyte stem cells become increasingly “stuck” in the bulge.

When McSCs become stuck in the bulge, they can no longer receive the signals that would cause them to specialize into melanocytes. At the same time, they lose their ability to function as stem cells, meaning they can’t specialize for future hair growth either.

“It is the loss of chameleon-like function in melanocyte stem cells that may be responsible for graying and loss of hair color,” said Dr. Ito in describing the study’s findings. “Chameleon-like function” refers to the McSCs’ ability to move between the two hair follicle compartments and specialize when needed. When cells lose this ability, hair begins to turn gray.

To test this idea, researchers artificially aged mice by repeatedly plucking their hair and forcing regrowth over the course of two years. Before plucking began, only about 15 percent of hair follicles had McSCs stuck in the bulge; by the end of the two years, that figure had risen to nearly 50 percent.

These stranded cells were unable to specialize or regenerate, and the affected hair turned gray.

Why Hair Keeps Growing But Loses Color

One notable finding was that hair kept growing even as McSCs became dysfunctional. That’s because the cells responsible for hair growth are different from the McSCs responsible for its color.

Hair follicle stem cells move in a single direction as they differentiate, rather than shuttling back and forth the way McSCs do — so even when McSCs stop working, hair follicle stem cells can keep producing new hair.

Dr. Qi Sun, a postdoctoral fellow at NYU Langone Health and the study’s lead investigator, described the significance of the discovery: “Our study adds to our basic understanding of how melanocyte stem cells work to color hair.

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.”

This back-and-forth mobility is unique to McSCs — other self-renewing stem cells, including those that drive hair growth, only ever move in one direction and never revert to an earlier state the way McSCs do.

What This Discovery Means for the Future

This study could change how scientists understand and approach hair graying. If researchers find a way to restore normal function to McSCs, it may become possible to prevent — or even reverse — the process.

Dr. Ito has described what comes next: “The next step is to look into ways to restore motility to these cells or to find ways to make these cells move. It may also be possible to develop a drug that will reactivate the cells.”

She added: “These findings suggest that melanocyte stem cell motility and reversible differentiation are key to keeping hair healthy and colored.” “Reversible differentiation” refers to the McSCs’ ability to become specialized cells and then return to being stem cells.

Although this study was conducted in mice, researchers believe the same mechanism is likely at work in humans, since McSCs are also present in human skin. That said, the research is still in its early stages.

Rui Yi, a stem cell biologist at Northwestern University’s Feinberg School of Medicine who was not involved in the study, has cautioned that meaningful biological differences between mice and humans make it unclear how directly these findings will translate — a question the research team itself is still working to answer.

Confirming the mechanism in humans, and then developing a medicine capable of restoring McSC function, would both be necessary before any treatment could become a reality.

For now, hair graying remains a natural part of the human aging process. But this study reframes it as the outcome of a specific, identifiable cellular mechanism — one that scientists are actively working to understand and, they hope, eventually overcome.