Androgenetic alopecia is a common genetic condition that causes hair loss in both men and women. This happens because of a strong reaction to androgens, which are hormones in the body. About 50% of men and women experience this condition, often starting any time after puberty. In men, hair loss usually occurs at the top and front sides of the head. For women, the front hairline is generally unaffected, but hair thinning happens on the top and crown of the head, often creating a wider part of the hair.