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.

How it affects hair and skin

Because DHT acts more strongly than testosterone on hair follicles and oil glands, higher enzyme activity in the skin can make androgen effects more noticeable in specific places. This is why some women have stubborn acne, oily skin, or thinning at the crown of the scalp even when blood tests show only moderate hormone levels, while facial and body follicles may respond with coarser hair. How sensitive the tissue is to androgens varies from person to person and is shaped partly by family background, so two people with similar testosterone levels can have very different experiences. You can read more about hormone-related signs on the hormones and PCOS symptoms pages.

What is usually discussed with a doctor

Some treatments that target androgen effects work by reducing this enzyme’s activity or blocking androgen action in tissue, but such approaches only suit some people and need a doctor’s assessment. No medicine decision should be made on your own without professional advice. A doctor weighs your symptoms, health history, and preferences, including whether you are planning pregnancy, because some medicines are not suitable then. For many people, lifestyle steps that support overall hormone balance are also discussed as part of a broader picture, rather than as a quick fix.

This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.