Most cysts are “functional.” They’re a part of your monthly cycle.
Follicle cyst. Your ovaries usually release one egg each month. It grows inside a tiny sac called a follicle. When the egg is ready, the follicle breaks open and releases it. If the sac doesn’t open, it causes a follicle cyst. These often go away in 1 to 3 months.
Corpus luteum cyst. Once the egg is released, the empty follicle usually shrinks and helps get ready for the next egg. It becomes a cyst when it closes back up and fluid collects inside. It may go away in a few weeks. But it may bleed or cause pain as it grows.
Others are nonfunctional. In some women, their ovaries make a lot of small cysts. This condition is called polycystic ovary syndrome (PCOS). It can make it hard to get pregnant. Other nonfunctional cysts may be caused by cancer. Ovarian cysts in women after menopause (once your period has stopped) are more likely to be cancerous than those in younger women.