Cellular and developmental aspects of androgenetic alopecia.

The hair follicle is a highly complex system that can be investigated at many levels and from multiple perspectives. However, underlying the cyclic production of all hair fibres are a set of common developmental processes. Many current investigations of androgenetic alopecia concentrate on the direct influences of hormones on hair follicles at the cellular or intracellular level. This paper attempts to step back from this and consider the process of terminal to vellus transition in androgenetic alopecia in terms of basic cellular and developmental mechanisms. Ideas about the mechanism and timing of follicle size reduction are put forward, but the paper also tries to point out inherent difficulties in the investigation of androgenetic alopecia and important gaps in current knowledge.