Male pattern hair loss (androgenetic alopecia) is a common condition in which men experience thinning of the hair on the scalp. This results in a receding hairline and/or balding on the top of the head. These changes typically begin gradually in men in their 20s. Over 25% of men in their 20’s experience male pattern baldness, while over 50% of men in their 50’s experience male pattern baldness.

Androgenic alopecia is the most common cause of baldness and hair loss in men and women. The two major factors in androgenic alopecia are genetics and hormones, specifically dihydrotestosterone (DHT). For a person to develop male pattern baldness, they need to have both of these factors present.

This was discovered from early studies looking at castrato (men castrated at an early age to forestall puberty and maintain a soprano vocal range). These castrato never developed hair loss, even if they had the genetic propensity to do so, because they did not have the other key factor, testosterone. A study group of the castrato was given testosterone at age 50 and the castrato with a genetic propensity developed male pattern baldness.

Recently we discovered it was not testosterone that caused hair loss, but a break down product of testosterone called dihydrotestosterone (DHT). This was discovered in a family with a genetic defect in Alpha-5 Reductase. Alpha-5 Reductase is the enzyme that breaks down testosterone into DHT. Without this enzyme, the male members of that do not produce DHT and they never go bald.


For many men, the hair in front or on top of their scalp has been “genetically programmed” to miniaturize at a predetermined time in their lives under the influence of DHT. The hair on the sides of the head (the “Friar Tuck” pattern) has a different genetic program, is not susceptible to DHT, and therefore grows forever. The balding areas do not represent “bad soil” or “diseased scalp,” they are simply areas that are genetically susceptible to the influence of DHT.