Why PCOS develops. The exact cause is still unknown, so this chapter looks at the factors research has linked to it and how they feed into one another: family history and genetics, insulin resistance (which is common even in women who are not overweight), high androgen levels, chronic low-grade inflammation, and environmental and lifestyle influences such as diet and exposure to pollutants. It explains how these factors can create a cycle that keeps symptoms going and makes ovulation and pregnancy harder.