What causes hair to go grey, and how stem cells could restore colour

A new study finds that hair turns grey when pigment stem cells get trapped inside follicles instead of moving to the colour-making zone, revealing a potential path to reversal

Grey hair may not be permanent after all. Scientists have discovered that the colour-fading process happens when pigment stem cells get “stuck” inside hair follicles instead of moving to the zone that produces colour.

 

The study, published in Nature and titled Dedifferentiation maintains melanocyte stem cells in a dynamic niche, suggests that restoring these cells’ mobility could one day make it possible to naturally reverse grey hair.

What causes hair to turn grey?

According to researchers from NYU Langone Health, the culprit is not ageing itself but the movement — or lack of it — of specialised pigment stem cells known as melanocyte stem cells (McSCs). These cells generate melanocytes, which produce melanin, the pigment that gives hair its colour.

 

 

In a healthy follicle, McSCs constantly shift between two zones: one that keeps them dormant and another that activates them to produce colour during a new hair growth cycle. Over time, however, these stem cells can become trapped in the “safe” zone, unable to travel back to the pigment-producing area. When that happens, hair still grows, but without its natural colour, turning grey or white.

What did the scientists discover?

Using advanced live imaging and single-cell RNA sequencing in mouse hair follicles, researchers tracked how individual pigment stem cells behaved over multiple growth cycles. They found that when hair was forced to regrow repeatedly, more McSCs became immobilised in the wrong compartment of the follicle.

 

This disrupted movement meant fewer pigment-producing melanocytes were generated, resulting in grey strands. In other words, the greying process is caused not by the death of pigment cells but by their failure to “commute” within the follicle.  ALSO READ | She wanted to dye her hair like K-pop stars. She got kidney disease instead

How pigment stem cells keep hair youthful

The researchers say their findings overturn the long-held belief that pigment stem cells are either permanently active or permanently dormant. Instead, these cells are far more dynamic, capable of switching between states and even reverting from mature pigment-producing cells back into stem cells, a process known as dedifferentiation.

 

This unique ability could be harnessed to restore colour to greying hair. If scientists can find ways to nudge these stranded stem cells to move again or reactivate the signalling cues that guide them, natural pigmentation might return without dyes or chemicals.

What does this mean for future treatments?

While the findings are still at the experimental stage, the implications are significant. By understanding and potentially manipulating the WNT signalling pathway, which helps pigment cells mature, researchers could develop therapies to rejuvenate hair colour.

 

Rather than forcing hair to grow or flooding follicles with artificial pigments, future treatments might revive the natural colour-making process by restoring proper cell movement. The goal, say the scientists, isn’t to permanently “switch on” pigmentation, but to keep the rhythm of regeneration balanced, some cells producing colour now while others stay in reserve.

Could this lead to a cure for greying?

Not immediately, as the study was conducted in mice, though human hair follicles share a similar structure and behaviour. Further research will be needed to confirm whether the same mechanisms operate in people.

 

Still, the discovery offers real hope. It suggests that grey hair is not necessarily a sign of damage or decline, but a timing issue, one that science may soon be able to fix. 

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