Hair loss occurs in both men and women, but the causes can be divergent. This is quite important, because treatment options depend closely on causative factors.
It is normal to shed some hair each day as part of this cycle. However, some people may experience excessive (more than normal) hair loss. Hair loss of this type can affect men, women and children. Hair Loss as been the most common cause by far is male pattern baldness, or androgenetic alopecia. This is the common hair loss pattern that is dependent on genetic predisposition, androgens (male hormones), and the simple passage of time.
These men have increased levels of a hormone known as 5(alpha)-reductase, which transforms testosterone into dihydrotestosterone (DHT). The DHT, in turn, causes follicles to sprout shorter,
finer hairs, before eventually dying out. It also causes the growth phases of hair follicles to become shorter, and the other phases to be longer. This usually results in the common Norwood pattern of loss, consisting of hair line recession, with or without loss in the crown.
Sometimes, acute stress to the system (such as high fever, sudden weight loss, etc.) produces a sudden, rapid shedding of hair, where you find clumps of hair coming out all over the place. Although this syndrome (called telogen effluvium) is alarming, it actually is good news, because the body readjusts itself and most if not all the hair grows back. People whose loss of hair is inherited notice their hair is thinning but don't see very much hair actually coming out.
Most men will loose hair in some point during their lives. Seventy percent of adult males will experience some degree of balding, and advanced male pattern baldness affects well over one half of the adult male population.
Men who suffer from androgenetic alopecia will experience hair loss in a younger age and until age 60 will loose anywhere between 30-90% of their hair. While boys have a straight low hair line, adult men have more of an "M"-shape.
Male pattern baldness is dependent on the interaction of three factors: age, a genetic pre- disposition, and male hormones, Once male pattern baldness begins, it does not stop.
The progression of male pattern baldness is generally classified on the Hamilton-Norwood scale, which ranges from stages I to VIII (see example)