PCOS isn’t something you catch or develop from a single cause. It’s a hormonal condition driven by a combination of genetics, insulin problems, and inflammation, with environmental exposures possibly playing a role. About 10 to 13% of women of reproductive age have it, making it one of the most common endocrine disorders. Understanding what drives PCOS helps explain why it looks different from person to person and why some people develop it while others don’t.
Genetics Account for Most of the Risk
The strongest factor behind PCOS is your DNA. Twin studies estimate that roughly 79% of the variation in who develops PCOS comes down to genetic influences, with no significant contribution from shared family environment (like growing up in the same household). That means if your mother or sister has PCOS, your own risk is substantially higher.
No single gene causes PCOS. Instead, it follows a polygenic pattern, meaning dozens of genes each contribute a small amount of risk. These include genes involved in androgen production, how your body responds to insulin, and how ovarian follicles develop. Researchers have identified links to genes that help convert cholesterol into androgens and genes that regulate follicle growth, but no consistent “PCOS gene” has emerged. This is why the condition runs in families without following a simple inheritance pattern.
Insulin Resistance Is a Central Driver
Even if genetics load the gun, insulin resistance often pulls the trigger. When your cells stop responding efficiently to insulin, your pancreas pumps out more to compensate. That excess insulin doesn’t just affect blood sugar. It directly stimulates your ovaries to produce more androgens (often called “male hormones,” though everyone has them). It also suppresses a protein made in the liver that normally binds to testosterone and keeps it in check. The result: more testosterone circulating freely in your blood.
High insulin also disrupts signals from your brain to your ovaries. The hypothalamus, which acts as a hormonal control center, begins releasing its signaling hormones too frequently. This tips the balance between two key reproductive hormones. Luteinizing hormone (LH) climbs too high relative to follicle-stimulating hormone (FSH). When LH dominates, your ovaries get the signal to make androgens instead of maturing eggs properly, which is why many people with PCOS have irregular or absent periods.
Insulin resistance is present in the majority of people with PCOS, but not all. It’s more pronounced in those who carry extra weight, yet it can also appear in people at a normal weight. This is a crucial point: you don’t need to be overweight to have the metabolic dysfunction that fuels PCOS.
Chronic Inflammation Adds Fuel
Low-grade, persistent inflammation plays a quieter but important role. People with PCOS tend to have elevated levels of inflammatory molecules in their blood and even in their ovarian fluid. These molecules interfere with normal ovarian function in several ways. They impair the growth and health of granulosa cells (the cells that surround and nourish developing eggs), reduce estrogen production, and create oxidative stress inside the follicle. Over time, this creates a self-reinforcing loop: inflammation disrupts hormone production, which worsens the hormonal imbalance, which sustains more inflammation.
Inflammation also reaches the brain. Animal studies show that the same inflammatory molecules found in ovarian fluid are elevated in the hypothalamus, where they can alter the pulsing rhythm of reproductive hormones. This contributes to the elevated LH levels that drive androgen excess. Immune cells from outside the ovary can migrate in and amplify these inflammatory signals, making the ovary itself a site of ongoing low-level immune activity.
You Can Have PCOS at Any Weight
There’s a persistent misconception that PCOS is caused by being overweight. While excess body fat can worsen insulin resistance and amplify symptoms, plenty of people develop PCOS at a normal BMI. This is sometimes called “lean PCOS,” and it has its own distinct pattern.
In lean PCOS, the hormonal control center in the brain tends to be more dysregulated, producing a more pronounced imbalance between LH and FSH. The adrenal glands also appear to be overactivated, producing more of an androgen precursor called DHEA-S, which gets converted into stronger androgens in other tissues. People with lean PCOS may have mild insulin resistance or abnormal cholesterol levels that don’t show up as weight gain but still drive the condition from the inside. This is why dismissing PCOS because someone “doesn’t look like they have it” misses the biology entirely.
Environmental Exposures May Play a Role
A growing area of research points to endocrine-disrupting chemicals as possible contributors, particularly when exposure happens before birth. These are synthetic chemicals that mimic or interfere with hormones. Three classes have drawn the most attention in relation to PCOS:
- Bisphenol A (BPA): Found in some plastics and food packaging. In animal studies, maternal BPA exposure altered postnatal development and the timing of sexual maturation in offspring.
- Phthalates: Common in personal care products, vinyl, and food packaging. Gestational exposure to certain phthalates produced polycystic ovaries and PCOS-like hormone profiles in rodent studies.
- Androgenic chemicals: Substances including nicotine and an antibacterial compound once common in soaps can create a high-androgen environment in the womb, potentially programming the fetus for hormonal problems later.
The human evidence is still emerging, but the hypothesis is straightforward: if a developing fetus is bathed in chemicals that disrupt hormone signaling during critical windows, the ovaries and hormonal systems may develop differently. This could help explain why PCOS sometimes appears in people with no family history of the condition.
How PCOS Gets Diagnosed
Diagnosis follows what’s known as the Rotterdam criteria, updated most recently in 2023. You need at least two of three features: signs of excess androgens (like acne, excess hair growth, or elevated testosterone on a blood test), irregular or absent ovulation, and polycystic-appearing ovaries on ultrasound. A newer option allows a blood test measuring anti-Müllerian hormone (AMH) to replace the ultrasound.
The “two out of three” requirement means PCOS can look very different between individuals. One person might have regular periods but significant acne and cystic ovaries. Another might have irregular cycles and high testosterone but normal-looking ovaries. This variability is part of why it takes an average of two years and multiple doctors before many people get a diagnosis.
Long-Term Health Risks
PCOS isn’t just a reproductive issue. The same insulin resistance and inflammation that cause the syndrome also raise the risk of serious metabolic problems over time. According to the CDC, more than half of people with PCOS develop type 2 diabetes by age 40. Heart disease risk is also elevated and increases with age.
These risks exist even in people whose day-to-day symptoms feel manageable. The hormonal and metabolic disruption is happening below the surface regardless of whether periods are irregular or skin is breaking out. This is why understanding what drives PCOS matters beyond just managing visible symptoms. The underlying insulin resistance and inflammation are worth addressing on their own terms, through movement, dietary changes that stabilize blood sugar, stress management, and in some cases medication, because they shape long-term health outcomes well beyond the reproductive years.