The genetically programmed hair growth cycle and alopecia: what is there to know?

Although commonly dismissed as being of superficial importance, the hair follicle is one of human biology’s most fascinating structures. One should not diminish the role of hair as a social and sexual communication signal in humans, as evidenced by the significant psychological trauma associated with its absence from the human scalp. Along with skin pigmentation, the hair fiber contributes much to the phenotypic variation between different human populations and can be significantly altered in its appearance. The last 20 years have seen a vast change in research activity into the regulation of hair growth in health and disease and, over the next 5 years, this should include further important glimpses of the nature of the hair follicle’s clock machinery (e.g., identification of the stop/start signals and triggers). Therapeutic and cosmetic manipulation of this mini organ will require a careful balance between delivery to the follicle of stimuli that are as specific as possible, while leaving other systems a...