It's the tell-tale sign of aging that men and women have tried to cover for generations. But scientists are one step closer to finding a way to reverse greying hairs without resorting to regular trips to the hairdresser. A team of researchers has discovered stem cells ?" which are able to develop into many different cell types ?" have the unique ability to move between growth compartments in hair follicles. As we age, these stem cells become stuck in a compartment called the hair follicle bulge. These 'stuck' cells are unable to regenerate into pigment cells, which help hairs keep their color, resulting in the hair turning grey.