The role of genetic predisposition and the influence of sex steroid hormones are indisputable to the pathogenesis of male androgenetic alopecia (MAGA). The role of sex steroid hormones in female pattern hair loss (FPHL) is less known. A good knowledge of the pathophysiology underlying MAGA and FPHL empowers the clinician to confidently counsel patients and make informed therapeutic decisions. Vigorous research in recent years has provided greater insight into the role of genetics and sex steroids in physiological hair growth and cycling, as well as in hair follicle miniaturization, the histological hallmark of MAGA and FPHL. In the present review article directed towards clinicians, we discuss the current understanding of the role of androgens and oestrogens, as well as genetic associations with MAGA and FPHL. We also briefly discuss the interpretation of direct-to-consumer genetic testing for baldness to help clinicians understand the limitations of such tests.

Review CMAJ• Inflammation that destroys the bulge of the outer root sheath destroys the hair follicle and leads to cicatricial alopecia.• Primary cicatricial alopecia is an inflammatory disorder of unknown cause that leads to irreversible hair loss.• The natural history is for the alopecia to extend slowly over the scalp and eventually burn out. The rate of extension and the final severity are extremely variable and difficult to predict.• A number of treatments are used empirically; however, they are not supported by data from clinical trials.