1 The regulatory biology of the human pilosebaceous unit

The last few years have witnessed an acceleration in our understanding of the regulation of the human pilosebaceous unit. Recombination and histochemical experiments are beginning to elucidate the role of homeotic genes, transcription factors, growth factors and adhesion molecules in pilosebaceous embryology. Histochemical studies, experiments in genemodified animals, and in vitro studies on growing human hairs, have identified a number of growth factors that are central to normal hair growth. Thus epidermal growth factor and transforming growth factor-α appear to be involved in the triggering of both anagen and categen. Insulin-like growth factor-I appears to sustain normal anagen growth, transforming growth factor-β will inhibit anagen growth, while interleukin-1-α and tumour necrosis factor-α will induce matrix cell death. These complex growth factor effects are beginning to be moulded into an integrated model of pilosebaceous regulation. The role of steroid hormones in modulating these growth factor effects is also beginning to be understood.