Most cases of hair loss are due to androgenetic alopecia (AGA). Fifty percent of men by age 50 years and 40% of women by menopause have some degree of AGA. Hair loss is gradual, with miniaturization of genetically programmed hair follicles. Uptake, metabolism, and conversion of testosterone to dihydrotestosterone by 5-alpha-reductase is increased in balding hair follicles. AGA appears different in men as compared with women. In men with AGA, hair loss occurs in the fronto-temporal regions and on the vertex of the scalp, depending on severity. In female AGA patients, it is more diffuse and located centroparietally. More......