Polycystic ovary syndrome, commonly abbreviated to PCOS, is a complex hormonal and metabolic condition associated particularly with irregular or absent ovulation, increased androgen activity and characteristic ovarian changes. Despite its name, the condition is not simply a disease of ovarian cysts. The small structures seen in many affected ovaries are usually follicles that have not progressed normally towards ovulation, rather than conventional pathological ovarian cysts.
A person can have PCOS without having polycystic-appearing ovaries on ultrasound, and having polycystic-appearing ovaries alone does not establish the syndrome. Current UK NHS terminology has begun using the name polyendocrine metabolic ovarian syndrome, or PMOS, to emphasise the endocrine and metabolic aspects, although PCOS remains the familiar and widely used term.
The reproductive component of PCOS involves disrupted follicle development and ovulation. In a typical menstrual cycle, several follicles begin developing and one generally becomes dominant and releases an egg. In PCOS, hormonal signalling can interfere with this process, so ovulation may occur infrequently or not at all. This can lead to irregular, widely spaced or absent menstrual periods because the normal cyclical hormonal changes associated with ovulation are disrupted. Anovulation also reduces the predictability of fertility, although pregnancy remains possible. The menstrual pattern is therefore an important manifestation of PCOS, but irregular periods can have many other causes and do not by themselves establish the diagnosis.
A second major feature is hyperandrogenism, meaning excessive androgen activity. Androgens are often informally called male hormones, but they are normal hormones in people with ovaries and are required in appropriate amounts for normal physiology. In PCOS, androgen concentrations may be elevated or tissues may be exposed to increased androgen effects. This can produce hirsutism, meaning excess coarse hair growth in androgen-sensitive areas such as the face, chest or abdomen, as well as acne and scalp hair thinning or loss. Some people have biochemical evidence of raised androgens without obvious outward symptoms, while others have clinical signs even when individual blood measurements are not dramatically abnormal.
The metabolic dimension of PCOS is closely linked to insulin resistance in many, although not all, affected people. Insulin is a hormone that helps cells take up and use glucose. With insulin resistance, the body may need to produce more insulin to maintain blood-glucose control. Higher insulin concentrations can interact with ovarian and adrenal hormone pathways and may contribute to increased androgen production, while androgen excess can further disrupt follicular development. This creates a biologically interconnected relationship between insulin signalling, ovarian function and androgen activity. Insulin resistance is therefore an important feature and risk pathway but is not synonymous with PCOS, and not every person with PCOS is insulin resistant or has excess body weight.
The term polycystic refers to ovarian morphology rather than the presence of ordinary ovarian cysts. Follicles are small fluid-containing structures in which eggs develop, and in PCOS numerous follicles may remain at an immature stage. On ultrasound, this can produce a characteristic appearance, sometimes described as a string of follicles. However, modern diagnostic approaches do not require this appearance if other diagnostic criteria are met.
This distinction is clinically important because telling someone that PCOS means they have ovarian cysts can create an inaccurate impression that the follicles are dangerous growths that need surgical removal. They are generally not equivalent to pathological ovarian cysts, which are a separate group of conditions.
PCOS can affect several aspects of health beyond menstruation and fertility. Associated features can include weight gain or difficulty losing weight, oily skin, acne, excess facial or body hair, scalp hair thinning, difficulty becoming pregnant and psychological symptoms such as anxiety or depression. People with PCOS can also have increased risks of metabolic problems such as impaired glucose regulation and type 2 diabetes, as well as other cardiovascular risk factors. The exact pattern varies considerably, so PCOS should not be understood as a single stereotyped appearance or symptom profile. A person can have PCOS while being lean, overweight or obese, and body size does not determine whether the syndrome is present.
Diagnosis generally depends on the overall clinical picture and exclusion of alternative explanations. In adults, a commonly used framework requires two of three broad features: irregular or absent ovulation, clinical or biochemical evidence of androgen excess, and polycystic ovarian morphology, after other relevant causes have been excluded. Ultrasound is therefore not automatically necessary. Blood tests may assess androgen levels and help exclude other endocrine disorders, while metabolic assessment can include blood pressure and testing for diabetes or abnormal cholesterol depending on individual circumstances. Diagnostic interpretation can be more complicated during adolescence because irregular cycles and acne can be normal features of puberty, so age and developmental stage matter.
PCOS is a syndrome rather than a single lesion, infection or temporary ovarian abnormality. The word syndrome indicates a recognisable cluster of interconnected features with multiple possible underlying mechanisms. There is no single cure that permanently removes every aspect of PCOS, but individual manifestations can often be managed effectively through lifestyle measures, hormonal treatments, medicines that improve metabolic or reproductive outcomes, and fertility treatments when pregnancy is desired.
Symptoms may change over the course of life, and menstrual or androgenic manifestations can alter after menopause. Understanding PCOS as an endocrine-metabolic-reproductive condition rather than simply as “cysts on the ovaries” is important for interpreting symptoms, diagnosis, fertility, long-term health risks and treatment choices accurately.
