Although it is universally accepted that dihydrotestosterone causes baldness, how it does so is not well understood. I propose that 3 mechanisms are at work: miniaturization by a dihydrotestosterone-induced acceleration of the mitotic rate of the matrix that leaves less and less time for differentiation; an increased telogen shedding as a result of the shortening of the hair cycles that increases the telogen number per unit of time; and the increased number and duration of the lag phase or kenogen. That this last mechanism is related to dihydrotestosterone is unclear.