Describe the role of DHT in androgenetic alopecia.

• A. Dihydrotestosterone (DHT) produced by 5-alpha-reductase leads to follicular miniaturization
• B. Estrogen is the main driver
• C. Alopecia is purely genetic with no hormonal influence
• D. Thyroid hormones cause all hair loss

Answer: (A)

Dihydrotestosterone (DHT) acts on scalp hair follicles to drive the pattern of thinning seen in androgenetic alopecia. DHT is produced from testosterone by the enzyme 5-alpha-reductase, especially the type II form present in hair follicles. Once formed, DHT binds with high affinity to androgen receptors in dermal papilla cells, triggering changes in gene expression that shorten the anagen (growth) phase and promote follicular miniaturization. Over time, many terminal hairs become smaller, producing shorter, finer hairs and a noticeable reduction in hair density—this is the miniaturization process that characterizes the condition. Genetic differences in follicle sensitivity to DHT explain why some people are affected more than others. This explains why reducing DHT production (for example, with a 5-alpha-reductase inhibitor) can slow or partially reverse the process. Statements attributing hair loss to estrogen alone, to thyroid hormones causing all hair loss, or to genetics without hormonal influence do not fit the established mechanism, since the hormonal action of DHT on susceptible follicles is the central driver.