The estimated rate of inheritance of male hair loss is 81%. This means that genetic factors contribute more to the risk of male baldness than environmental factors. Hereditary predisposition is the most powerful factor for hair loss in men; the genes largely determine whether a man will show male pattern hair loss, the age of its onset, the pattern and the degree of progress.
Patterns of Male Hair Loss
The most common pattern of androgenetic alopecia is the frontal and temporal thinning, with a tendency to extend to the crown of the head. Over the years, the thin area on the crown of the head expands and in many cases ultimately unites with the front area. Hair loss with apparent thinning occurs in 25% of the male population by the age of 30 and in 50% by the age of 45-50. There is strong evidence that the pattern and the development speed of alopecia in each man has a hereditary background. The stages of progression of hair loss in men is reflected in the Hamilton-Norwood scale for androgenetic alopecia.
Men suffering from androgenetic alopecia inherit hair follicles that are genetically susceptible to the hormone dihydrotestosterone (DHT). Dihydrotestosterone (DHT) is a derivative or by-product of testosterone. Testosterone is converted to DHT by means of the enzyme 5-alpha-reductase, which enters the follicles, shrinks the follicles and causes changes in their function, suppressing their growth. The hair follicles that are sensitive to the DHT hormone become thinner and their lifespan is reduced, resulting in shedding of the hairs and reduced density on the scalp.
More specifically, the action of the hormone DHT shortens the anagen (growing) phase of the hairs and expedites the telogen phase, in which the development stops. This process weakens the hairs, ultimately resulting in shedding. Men who show the first signs of thinning usually display a picture in which the loss of hair density is not due to shedding, but rather the progressive thinning of the hair shafts. The hair follicles gradually degenerate, the life cycle of the hair is shortened, and every new hair that is produced becomes increasingly thinner and weaker, with an ever shorter life span. This occurs at a speed that differs from one man to another, until the follicle reaches its final stage of degeneration, in which the hair appears thin and transparent like fluff.
Male hair loss in most patients starts at the end of puberty and progresses rapidly in the ages between 20-30, while the shedding slows down after the age of 30-35. At higher ages, the hair loss is slowed down even further, following a path that coincides with the stabilisation and gradual decline in levels of male hormones in the blood.