Polycystic ovary syndrome (PCOS) causes harmless cysts in the ovaries and also causes other symptoms. PCOS is caused by certain hormones being out of balance. The word “syndrome” means a group of symptoms. Women with PCOS may have no periods, irregular periods, or very long periods.

Your Ovaries

A woman’s ovaries are where her eggs are stored. Each egg is in a capsule called a follicle. Each month, one follicle grows to produce a mature egg. This egg is released (ovulation) and the follicle dissolves.

Hormones out of Balance

With polycystic ovary syndrome (PCOS), the chemicals (hormones) that control ovulation are out of balance. These include estrogen and androgen (a male hormone). As a result, ovulation may not occur. Instead, the follicle stays enlarged. This is a cyst (fluid-filled sac). Over time, the ovaries fill with many cysts. This is why they are called “poly” (many) “cystic” ovaries. In some women, the ovaries also make too many male hormones.