Cyclosporin A prolongs human hair growth in vitro

We studied the effect of cyclosporin A on human hair growth using a recently described model in which isolated hair follicles are grown in vitro. Cyclosporin A had no effect on the rate of hair growth, but at 10(-7) M, a dose within the therapeutic blood range, it maintained hair growth for longer than control to give a 42% greater mean follicle elongation after 15 d (p < 0.05). Eighteen of 42 cyclosporin-treated follicles (43%) were still growing after 15 d compared with one of 42 control follicles (2%). These results suggest that the hypertrichotic action of cyclosporin A may be due to prolongation of the anagen phase of the hair-growth cycle.