What is PCOS? Causes, types and the long-term picture.

PCOS is a common, lifelong condition that affects how the ovaries work, how the body handles insulin, and how much androgen (the “male-type” hormones every woman makes in smaller amounts) circulates. The World Health Organization estimates it affects 10–13% of women of reproductive age, and a meta-analysis found prevalence as high as about 10% under the widely used Rotterdam criteria.

Why the name is misleading

“Polycystic ovaries” sounds like the ovaries are full of cysts. They aren’t. On ultrasound, what you see are many small follicles — the fluid-filled sacs that each hold an egg — that started developing and then stalled before one could mature and release. Some people with PCOS don’t have this ultrasound appearance at all, and some people without PCOS do. Experts have long debated renaming the condition for exactly this reason.

What causes PCOS?

There is no single cause. Researchers describe PCOS as the result of several interacting factors:

• Genetics. PCOS runs strongly in families, and several susceptibility genes have been identified. Having a mother or sister with PCOS — or a family history of type 2 diabetes — raises the likelihood.
• Insulin resistance. Many people with PCOS have tissues that respond poorly to insulin, independent of body weight. Higher insulin levels stimulate the ovaries to make more androgens and reduce sex-hormone-binding globulin (SHBG), so more testosterone circulates freely. More on the insulin connection →
• Hormone signalling. The brain’s signals to the ovaries are often altered in PCOS, with relatively high luteinising hormone (LH), which also drives androgen production.
• Developmental factors. Research suggests exposure to higher androgens before birth may play a role in programming the condition.

Lifestyle doesn’t cause PCOS, but weight gain can amplify its expression, and lifestyle changes can soften it.

How PCOS is diagnosed

The 2023 international guideline keeps the Rotterdam framework: PCOS is diagnosed in adults when at least two of these three are present, and other causes have been excluded (such as thyroid disease, high prolactin and non-classic congenital adrenal hyperplasia):

1. Irregular cycles or ovulatory dysfunction — for adults, cycles shorter than 21 or longer than 35 days, or fewer than eight periods a year.
2. Hyperandrogenism — clinical signs (excess hair growth, acne, scalp hair thinning) or raised androgens on blood tests.
3. Polycystic ovarian morphology on ultrasound — or, new in 2023, a raised anti-Müllerian hormone (AMH) level in adults.

If you have both irregular cycles and high androgens, you don’t need an ultrasound to be diagnosed. In adolescents, the rules are stricter: both irregular cycles and hyperandrogenism are needed, and ultrasound isn’t used within eight years of the first period. Our PCOS blood test guide walks through each test.

The four types of PCOS (phenotypes)

Because you need two of three features, there are four combinations. These are the evidence-based “types of PCOS” — not the internet’s “adrenal PCOS” or “inflammatory PCOS” labels, which aren’t recognised diagnostic categories.

“Lean PCOS” isn’t a separate type — it’s PCOS in someone with a lower BMI. It’s common, and insulin resistance can still be present. If your symptoms seem to fit, the symptom quiz shows where they cluster.

Why PCOS is more than a reproductive condition

PCOS is often first noticed through periods, fertility or skin. But the guideline emphasises its broader features:

• Metabolic: higher risk of insulin resistance, prediabetes, type 2 diabetes, gestational diabetes and unfavourable cholesterol.
• Cardiovascular risk factors: blood pressure and lipids deserve regular checks.
• Sleep: obstructive sleep apnoea is more common.
• Endometrial health: very infrequent periods let the uterine lining build up, which is linked to a higher (though still low in absolute terms) risk of endometrial cancer.
• Mental health: depression, anxiety, body-image concerns and disordered eating are significantly more common, so screening and support belong in routine care.

What to do next

A diagnosis is a starting point. Read how to manage PCOS for the full plan, then dig into the cluster that matters most to you — symptoms, diet, periods or fertility.

PCOS across life stages

PCOS isn’t only a “reproductive years” condition. In adolescence, diagnosis is cautious because irregular cycles are normal after the first period. Through the 20s and 30s, cycles, fertility, skin and weight usually dominate. Cycles often become more regular in the late 30s and 40s. After menopause, the cycle criteria no longer apply, but metabolic and cardiovascular risk factors remain relevant, so screening continues.

Common myths about PCOS

• “You can’t get pregnant with PCOS.” Most people with PCOS who want children can conceive, often with simple treatment. See PCOS and fertility.
• “Only overweight people get PCOS.” PCOS occurs at every size.
• “The pill cures PCOS.” It manages symptoms while you take it; it doesn’t change the underlying condition.
• “PCOS means you have ovarian cysts that need removing.” The follicles seen on ultrasound aren’t true cysts and don’t need surgery.
• “There’s nothing you can do.” Many effective options exist — see how to manage PCOS.