The exact reasons why PCOS develops aren't fully understood at present. Several factors seem to be important. PCOS runs in some families, so there may be a genetic link. High levels of certain hormones may also cause PCOS. Eg, you may have resistance to insulin, the hormone that controls your blood sugar level. This means the level of insulin in your blood needs to be higher than normal to control your blood sugar level. The extra insulin may cause your ovaries to make too much testosterone, which can lead to excess hair and acne. Increase in testosterone can also stop ovulation. If you have excess body fat, this can make insulin resistance and the symptoms of PCOS worse.
Attribution: BUPA