Viable terminal scalp hair follicles constitute a necessary and sufficient biological end-organ that conditions clinical efficacy of finasteride in males with male pattern hair loss without implying reversal of miniaturized follicles.

BACKGROUND: Biopsy-based "reversal hypothesis" claimed conversion of miniaturized hair follicles into terminal ones for the improvement of male pattern hair loss (MPHL) with FDA-approved drugs.

MATERIALS AND METHODS: MPHL volunteers (n = 13) completed a 24-month phototrichogram study. After 2 months no-treatment, panellists took finasteride 1mg daily for 2 years. Hair changes from the best responder would explain the nature of improved hair growth.

RESULTS: Due to the wide range of hair growth variables, no parameter was statistically significantly changed by finasteride in the group. Clinically there were 4 worse, 6 no change, 2 slightly and 1 moderately improved subject associated with turning telogen/empty terminal follicles into anagen after 12- and 24-month finasteride. From 113 miniaturized hair (diameters ≤ 30 µm) at baseline, 79 were still miniature hair after 2 years on finasteride. No hair were found at the remaining mapped sites except for 2 terminal hairs considered a probabilistic "uncertainty."

CONCLUSION: Moderate hair improvement resulted from increased productivity of deficient terminal follicles, but not yet irreversibly affected at baseline without implication of miniaturized hair follicles. The latter further regressed even with oral intake of finasteride. The data suggest the rejection of the "reversal hypothesis" unless proven otherwise with duly validated methods.