Androgenic Alopecia

Androgenic alopecia (also known as androgenetic alopecia, alopecia androgenetica, male pattern baldness) is loss of hair that occurs due to an underlying susceptibility of hair follicles to androgenic miniaturization. It's the most common cause of hair loss and will affect up to 70% of men and 40% of women at some point in their lifetime. Men typically present with hairline recession at the temples and vertex balding while women normally diffusely thin over the top of their scalps. Both genetic and environmental factors play a role, and many etiologies remain unknown.

Classic androgenic hair loss in males begins above the temples and vertex, or calvaria, of the scalp. As it progresses, a rim of hair at the sides and rear of the head remains. This has been referred to as a 'Hippocratic wreath', and rarely progresses to complete baldness. The Hamilton-Norwood scale has been developed to grade androgenic alopecia in males.

Female androgenic alopecia has been colloquially referred to as 'female pattern baldness', although its characteristics can occur in males as well. It more often causes diffuse thinning without hairline recession, and like its male counterpart rarely leads to total hair loss. The Ludwig scale grades severity of androgenic alopecia in females.

Animal models of androgenic alopecia occur naturally and have been developed in transgenic mice, chimpanzees (Pan troglodytes), bald uakaris (Cacajao rubicundus) and stump-tailed macaques (Macaca speciosa and Macaca arctoides), of which the macaques demonstrate the greatest incidence and most prominent hair loss.