The cysts associated with PCOS develop during the process of ovulation. Every month, as part of a woman's normal cycle, the ovaries produce an egg. Most ovarian cysts form on the ovaries if the follicles (sacs) that contain the egg mature but do not release the egg into the fallopian tube. For women who have PCOS, the presence of cysts may ultimately prevent ovulation. In PCOS the cysts are multiple and often larger than usual.

Specific causes of PCOS are not known, but research suggests that excess insulin plays a role in many of the symptoms of PCOS. Excessively high levels of insulin in the body are thought to have the effect of preventing ovulation and causing a rise in so called “male hormones” or androgen (testosterone) levels. Excess androgen can result in symptoms such as long coarse hair on your face and body, acne, and male pattern baldness. However, not all women with PCOS have these symptoms.

PCOS is also often associated with Type 2 diabetes and obesity. It is generally believed that PCOS has a genetic component influenced by environmental factors such as diet and exercise, which is also often the case with Type 2 diabetes and obesity. Although it is unclear whether obesity causes PCOS or the other way around, some women find that their PCOS and diabetes symptoms disappear with weight loss, regular exercise, and a diet lower in fat and carbohydrates.

As PCOS is a group of symptoms rather than a single condition, cysts are not the only defining factor. Sometimes a doctor will diagnose PCOS when cysts are not present but many of the other symptoms are. Three very common symptoms are:

• Infrequent or irregular periods, often beginning in adolescence. “Irregular” means your cycle occurs at intervals of 35 days or longer or less than eight times a year. This is a result of an absence of ovulation or infrequent ovulation. 
• Increased levels of male hormones, such as testosterone. This often results in acne, oily skin or dandruff, male pattern baldness or thinning hair, and excess hair growth on the face, chest, stomach, thumbs or toes.
• Obesity. This is a factor in 50-60% of PCOS cases, but of course, that means 40-50% of women with PCOS are of normal weight. Weight gain may also be a symptom. Insulin resistance is common in PCOS and probably plays a role in weight gain.

Other symptoms include:

• Ongoing pelvic pain for more than six months
• Diabetes, over-production of insulin or inefficient use of insulin by the body
• High triglycerides
• High blood pressure
• High cholesterol
• Heart disease
• Skin tags or tiny excess flaps of skin in the armpits or neck area
• Infertility
• Difficulty becoming pregnant
• Acanthosis nigricans: darkened, velvety skin on the nape of your neck, armpits, inner thighs, vulva, or under your breasts