We don't really know what causes PCOS but most researchers think that more than one factor could play a role in causing PCOS. 

These factors include:

• Genetic predisposition
• Insulin resistance or hyperinsulinism (high blood levels of insulin)
• Obesity
• Hyperandrogenism (excessive production of male hormones).
• Abnormality of the hypothalamic-pituitary-gonadal axis (organ/hormonal disorder)
• Environmental chemical pollution (hormonal disruptors)
• Chronic inflammation