From infancy to old age, everyone loses hair every day as hair follicles go through their normal cyclic activity of anagen (growth phase), catagen (shedding phase) and telogen (resting phase). A full anagen-catagen-telogen cycle can take years to complete. Each follicle goes through the complete cycle 10 to 20 times over a normal human lifetime. At any given time, about 1% or fewer of scalp follicles are in shedding phase, which takes place when a new telogen (growth) phase begins. The average number of scalp hairs lost every day from a “full head of hair” due to normal catagen activity is variable, ranging up to 100 or more. Substantially more than 100 hairs lost per day is unusual and may indicate an abnormal shift in cycling activity. Each follicle is an independent unit, not acting in coordination with neighboring follicles but responding to the same growth control signals as neighboring follicles. Hair loss due to normal anagen-catagen-telogen cycling activity is usually recognized as normal by the individual man or woman; it is the amount of lost hair he or she is accustomed to seeing. Over the course of several cycles, this normal hair loss is recognized as temporary, the lost hair replaced by new growth from follicles that shift from telogen (resting) into anagen (growth) phase. If an unusually large number of lost hairs begin to appear in the course of grooming, or on one’s pillow or clothing, the “temporary” nature of the hair loss may be questionable. The person may begin to ask: “Am I beginning to lose hair permanently. Am I going bald?” The question may be especially stressful for men who have close male relatives with hair loss. Androgenetic alopecia (called male pattern baldness when it occurs in men) has a genetic basis-that is, it “runs in the family”. A man who knows he has a family history of androgenetic alopecia may worry about the daily loss of more hair than he is accustomed to observing. While a man who has a family history of male-pattern hair loss is at higher risk for androgenetic alopecia, a man cannot be sure that the hair loss he observes is an initial sign of male-pattern hair loss. In fact, many men do not begin to notice hair shedding until they begin to notice hair thinning on the scalp. Androgenetic alopecia is known to have a genetic basis, but the patterns of genetic inheritance have not been worked out with precision. A man may carry the gene or genes for androgenetic alopecia; it is difficult to predict whether he will experience balding. If relatively large daily loss of scalp hair continues over time, it becomes more likely that the man is developing the visible signs of male pattern baldness. A man in this position need not wait for evidence of a substantial permanent hair loss to seek advice or begin treatment, if he so desires.