Androgenetic Alopecia

Androgenetic alopecia (AGA) is the most common form of progressive hair loss, affecting approximately 50% of men by age 50 and 40% of women by menopause. It is driven by genetic sensitivity of hair follicles to dihydrotestosterone (DHT), which causes follicle miniaturization — progressive shortening of anagen phase and production of thinner, shorter vellus-like hairs. In men, it typically presents as frontal recession and vertex thinning (Hamilton-Norwood scale). In women, it presents as diffuse thinning of the crown (Ludwig scale). Multiple genes contribute to susceptibility, with the androgen receptor gene on the X chromosome being a major risk locus.