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 developmenta
l processes. Many current investigations of androgenetic alopecia conc
entrate 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 and
rogenetic alopecia in terms of basic cellular and developmental mechan
isms. Ideas about the mechanism and timing of follicle size reduction
are put forward, but the paper also tries to point out inherent diffic
ulties in the investigation of androgenetic alopecia and important gap
s in current knowledge.