Male Pattern Baldness (MPB) is the most common indication for hair transplantation. It is caused by the exposure of hair to the androgen Di-Hydro-Testosterone (DHT), a metabolite of testosterone created when testosterone reacts with the enzyme 5-alpha-reductase. When susceptible scalp hairs are exposed to DHT, they become finer and shorter with each recurring growth cycle, eventually leading to baldness.

The severity of MPB varies dramatically and can be as mild as minor recession of the hairline or as severe as the complete loss of hair on the superior aspect of the scalp. Genetically determined differences in the sensitivity to DHT explains these variations between people. However, even in the most severe case of MPB, hair loss does not occur in the horseshoe-shaped ring of hair in the occipital and lateral fringe areas of the scalp. This is because this hair is not sensitive to the effects of DHT.