Why do we go gray as we get older? I realized recently that I hadn’t the faintest idea. Fortunately, a thorough description of the role of melanocyte stem cells in this conspicuous phenotype of aging can be found in a review by Sarin and Artandi:

Hair graying is one of the prototypical signs of human aging. Maintenance of hair pigmentation is dependent on the presence and functionality of melanocytes, neural crest derived cells which synthesize pigment for growing hair. The melanocytes, themselves, are maintained by a small number of stem cells which reside in the bulge region of the hair follicle. The recent characterization of the melanocyte lineage during aging has significantly accelerated our understanding of how age-related changes in the melanocyte stem cell compartment contribute to hair graying. This review will discuss our current understanding of hair graying, drawing on evidence from human and mouse studies, and consider the contribution of melanocyte stem cells to this process. Furthermore, using the melanocyte lineage as an example, it will discuss common theories of tissue and stem cell aging.

Given the attention we pay to life-threatening maladies like wrinkling and baldness, I’m sure it’s only a matter of time before someone proposes “stem cell therapy” to rid us of this salt-and-pepper scourge.

UPDATE 11/15/2007: More on this at Mind Hacks.