How does testosterone or dihydrotestosterone play a part in hair growth or loss?

Hair loss: Two types of androgens are involved in the mechanism of male pattern hair loss. These are testosterone and dihydrotestosterone (dht). Dihydrotestosterone is a derivative of testosterone. The enzyme called 5-alpha reductase converts the relatively inactive testosterone to a more potent form, dihydrotestosterone. Thus, the key enzyme involved in androgenetic hair loss is 5-alpha reductase.