An enzyme that converts testosterone into DHT, a stronger androgen that affects hair and skin.
Why it matters for PCOS
5-alpha-reductase is an enzyme in tissues such as the scalp, hair follicles, and oil glands that converts testosterone into dihydrotestosterone (DHT), a more potent form of androgen. In PCOS, androgen-driven skin and hair symptoms, such as acne, excess facial hair (hirsutism), and scalp hair thinning, depend partly on how active this enzyme is in the local tissue. This helps explain why two women with similar blood testosterone levels can have very different skin and hair symptoms.
The enzyme is not usually measured directly in routine PCOS blood tests. Doctors assess overall androgen effect through symptoms and tests such as testosterone and SHBG, then plan treatment in that context.
This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.