What causes pattern balding?

Male pattern hair loss is an inherited condition, caused by a genetically determined sensitivity to the effects of dihydrotestosterone, or DHT in some areas of the scalp. DHT is believed to shorten the growth, or anagen, phase of the hair cycle, from a usual duration of 3–6 years to just weeks or months. This occurs together with miniaturisation of the follicles, and progressively produces fewer and finer hairs. The production of DHT is regulated by an enzyme called 5-alpha reductase.

Several genes are involved, accounting for differing age of onset, progression, pattern and severity of hair loss in family members. The susceptibility genes are inherited from both mother and father. At this time, genetic testing for prediction of balding is unreliable.

A few women present with male pattern hair loss because they have excessive levels of androgens as well as genetic predisposition. These women tend also to suffer from acne, irregular menses and excessive facial and body hair. These symptoms are characteristic of polycystic ovarian syndrome (PCOS) although the majority of women with PCOS do not experience hair loss. Less often, congenital adrenal hyperplasia may be responsible. Females that are losing their hair with age are more likely to present with female pattern hair loss, in which hormone tests are normal.