Male hair loss initially and typically affects the temples and the crown of the scalp, with hair either thinning or falling out. The progression of male pattern baldness is generally classified on the Hamilton–Norwood scale (first introduced by Dr James Hamilton in the 1950s and later revised and updated by Dr O’Tar Norwood in the 1970s).
Male pattern baldness is the cause of hair loss in men in more than 95% of cases. According to statistics, 25% of men begin balding by age 30 and two-thirds begin balding by age 60. Male pattern baldness is triggered by the sex hormone dihydrotestosterone (DHT), which is created from testosterone by the enzyme 5-alpha reductase. In those with a genetic predisposition to hair loss, DHT initiates a process of follicular miniaturisation. As the hair follicle deteriorates, the hair growth phase (anagen) is shortened, and the hair shaft is prevented from growing and maturing into the deeply rooted and pigmented hair. In time, hair becomes thinner. If left untreated the follicle will go dormant and stop producing hair completely.