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What causes PCOS?

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Researchers and health care providers know that genetic and environmental factors contribute to the development of PCOS, but do not know exactly what causes PCOS.

Because the symptoms of PCOS tend to run in families, the syndrome is probably caused, at least in part, by a change, or mutation, in one or more genes. Recent research conducted in animal models suggests that in some cases PCOS may be caused by genetic or chemical changes that occur in the womb.1

PCOS likely results from a combination of causes, including genes and environmental factors.

What causes the symptoms of PCOS?

Most of the symptoms of PCOS are caused by higher-than-normal levels of certain hormones, called androgens.

The ovaries produce hormones, which are chemicals that control functions in the body. One of the hormones that the ovaries make is estrogen—sometimes called the "female hormone" because women's bodies make more of it than men's bodies do. The ovaries also make androgens—sometimes called "male hormones" because men's bodies make more of them than women's bodies do. Men and women need certain levels of both hormones for normal health.

In women with PCOS, the hormones are out of balance: these women have higher-than-normal levels of androgens and may have lower-than-normal levels of estrogen. High levels of androgens can:

  • Interfere with signals from the brain that normally result in ovulation, so that ovulation does not occur regularly
  • Cause the follicles—small, fluid-filled cysts within the ovaries in which eggs grow and mature —to enlarge, forming cysts2
  • Produce other symptoms of PCOS, including excess hair growth and acne3,4

Other symptoms of PCOS result from problems with insulin, another of the body's hormones. Insulin helps move sugar (also called glucose) from the bloodstream into cells to use as energy. When cells don't respond normally to insulin, the level of sugar in the blood rises. In addition, the level of insulin goes up as the body produces more and more of it to try to get glucose into the cells. Too much insulin increases the production of androgens,5 which then cause symptoms of PCOS. High levels of insulin can also increase appetite and lead to weight gain.3 High insulin levels are also linked to acanthosis nigricans.3

  1. Goodarzi, M. O., Dumesic, D. A., Chazenbalk, G., & Azziz, R. (2011). Polycystic ovary syndrome: Etiology, pathogenesis and diagnosis. Nature Reviews Endocrinology, 7, 219–231. [top]
  2. National Center for Biotechnology Information, National Library of Medicine, PubMed Health. (2011). Polycystic ovary syndrome. Retrieved December 22, 2011, from [top]
  3. American College of Obstetricians and Gynecologists (ACOG). (2011). Polycystic ovary syndrome. Retrieved May 10, 2012, from External Web Site Policy (PDF - 273 KB) [top]
  4. American Society for Reproductive Medicine. (2003). Hirsutism and polycystic ovary syndrome: A guide for patients. Birmingham, AL: American Society for Reproductive Medicine. [top]
  5. Ehrmann. D.A. (2005). Polycystic ovary syndrome. New England Journal of Medicine, 352, 1223–1236. [top]

Last Reviewed: 05/23/2013
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