Researchers believe they have discovered the mechanism behind hair turning grey, potentially paving the way for treatments to reverse or prevent the process. The study suggests that as hair ages, certain stem cells called melanocyte stem cells (McSCs) lose their ability to mature and maintain hair color due to their reduced ability to transition between growth compartments in hair follicles. 

The study, led by scientists from New York University Grossman School of Medicine, focused on cells in the skin of mice and humans. If the findings hold true for humans, it may present a potential pathway for reversing or preventing grey hair by aiding the movement of jammed cells between developing hair follicle compartments. 

Source: https://www.theguardian.com/science/2023/apr/19/scientists-may-have-discovered-why-hair-turns-grey