article_snippet: Pigment production also turns on and off in rhythm with the hair cycle.
article_snippet: When pigment cells turn off at the end of one hair cycle and fail to turn back on with the onset of the next, hair becomes grey.
article_snippet: So, why doesn't pigment production turn back on?
article_snippet: If the melanocyte stem cell reservoir at the top of the hair follicle can replenish the bulb, this keeps pigment production going.
article_snippet: But when the reservoir of stem cells is exhausted, pigment production stops and the hair turns grey.
article_snippet: Scientists have long known that in order to prevent hair from going grey Scientists would need to either prolong the life of the melanocytes in the hair bulb – by protecting Scientists from injury – or expand the melanocyte stem cell reservoir in the upper or top region of the hair follicle so Scientists continue to replace lost pigment cells.
article_snippet: This enables pigment production to restart as soon as the next hair cycle begins.
article_snippet: But The agents won't re-colour grey hair or bring back the dead cells that produce hair colour.