How Hair Turns Gray

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We've all heard it before: Too much stress will give you gray hair.

While there seems to be some truth to that theory, the science behind our silvery strands has remained a mystery until now.

While examining interactions between two types of stem cells, a group led by New York University School of Medicine researchers discovered that the cells' collaboration through a specific signal determines pigmentation in hair follicles.

In essence, scientists discovered how hair turns gray.

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But the findings, featured in the journal Cell, extend beyond personal aesthetics. Knowing how these cells interact may also help researchers understand tissue regeneration or even ways to halt abnormal cell growth observed in conditions such as melanoma, a potentially fatal form of skin cancer caused by abnormal growth of one type of cell.

The two types of stem cells, melanocytes and epithelial cells, work together to build individual strands of hair, just like other tissues and organs in the body. Though many had a hunch the two groups of cells were involved in the graying of hair, the exact signal they use to coordinate — called the Wnt pathway — wasn't initially clear.

The team looked at the process in genetically modified mice rather than humans and wound up with some gray-haired rodents after manipulating the Wnt pathway. They confirmed their findings in mice stem cells, too.

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Over time, however, these stem cells responsible for producing hair follicles slow down or lose their ability to inject melanin into every strand, resulting in gray hair. Some cells in hair follicles seem to get exhausted faster than others, which explains why even young people can grow silver strands.

It's also suggested that stress places pressure on follicle-producing cells, hampering the process. But there's still debate surrounding whether stress is the primary factor.

Because scientists now know what limits melanin production and overall growth in adult hair, they can explore what works during normal pigmentation and growth. Perhaps other stem cells use similar mechanisms to keep the body healthy, too.

Studying this pathway may provide the clues needed to coax stem cells toward tissue regeneration in the lab, and potentially, in a patient's body later on.

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