A recent study found that some stem cells lose their capacity to mature and maintain hair color as people age because they become caught in the growth compartments of hair follicles.

The latest study, led by researchers from NYU Grossman School of Medicine, focused on cells called melanocyte stem cells, or McSCs, which are found in both human and mouse skin. Whether McSC pools within hair follicles receive the signal to mature into mature cells that produce the protein pigments responsible for color determines hair color.

The latest study, which was published online in the journal Nature on April 19 found that McSCs are remarkably malleable. This implies that these cells continuously proliferate during typical hair growth move back and forth on the maturity axis as they transit between compartments of the developing hair follicle. It is inside these compartments where McSCs are exposed to different levels of maturity-influencing protein signals.

Specifically, the research team found that McSCs transform between their most primitive stem cell state and the next stage of their maturation, the transit-amplifying state, and depending on their location.

The researchers found that as hair ages, sheds, and then repeatedly grows back, increasing numbers of McSCs get stuck in the stem cell compartment called the hair follicle bulge. There, they remain, do not mature into the transit-amplifying state, and do not travel back to their original location in the germ compartment, where WNT proteins would have prodded them to regenerate into pigment cells.