Androgenetic alopecia is a common disorder leading to hair loss; it is genetic or hereditary in origin. Hair falls out because the hair follicles or roots are too sensitive to Dihydrotestosterone DHT, a by-product of testosterone, the male hormone circulating in the blood. The hair on the crown of the head is protected from the effects of these hormones.

Up to two-thirds of Caucasian men between the ages of 35 and 40 are affected; women are affected to a lesser degree (around 30 % before menopause and more than 50% after the menopause).

In men, baldness is first manifested by the gradual withdrawal of the frontal line, followed by more or less extensive loss of hair to the tonsure. In women, it is rather manifested by a gradual and diffuse decrease in hair density over the entire head. The frontal line is usually not affected.

Hair loss is usually gradual, with periods of active loss alternating with periods of remission.

Generally speaking, if hair loss begins early in life, it will be more severe in later years.