Retinoids: compounds important to hair growth.

Although the mechanisms of follicular regression in androgenetic alopecia are not fully understood, retinoids may be important in changing the status of regressing follicles. There are many reports documenting reversal of epithelial dysplastic changes with retinoids. Although none of the studies with retinoids have concentrated on the precise mechanisms of follicular growth (regression or regeneration), these limited observations, and our early studies suggest that further work should be done on the effect retinoids have on the hair follicle during the various growth and regression phases of the follicular life cycle in humans. We propose that certain retinoids increase the rate of hair growth, prolong the anagen phase of the hair cycle, play a role in converting vellus to terminal hairs, and act synergistically with minoxidil to produce more dense hair regrowth from regressing follicles than either compound alone. Larger controlled studies and better methods for assessing hair growth are necessary to support these early results. Other retinoids as well as certain minoxidil analogs should also be studied.