Ovarian cysts, which are small fluid-filled sacs that develop in or on the ovaries, are very common and are usually harmless.

In fact, “the process of ovulation—maturing an egg and releasing it—basically makes at least a little cyst, which pops when the egg is released, and then these cysts resolve,” explains Dr. Mary Jane Minkin, an ob-gyn at Yale Medicine. These are often called “functional cysts,” and they usually go away on their own.

Other types of ovarian cysts include hemorrhagic cysts (which bleed and cause pain), dermoid cysts (which may contain skin cells and sebaceous glands), and endometriomas (which are filled with dark, thick blood and develop as a result of endometriosis). Ovarian cysts also can occur with polycystic ovary syndrome (PCOS), but they don’t always.

Here’s what to know about ovarian cysts.

How ovarian cysts affect women
Most ovarian cysts are the size of a grape or cherry and don’t cause symptoms. But cysts that grow quickly can cause pain in the pelvis near the hipbone and a feeling of persistent pressure. “This discomfort can be intermittent or constant and may feel sharp or dull,” says Dr. Kelli V. Burroughs, an ob-gyn at UT Health—University of Texas Medical School at Houston.

By contrast, cysts that rupture or burst can cause intense pelvic pain and sometimes slight bleeding, says Minkin. “The pain will get better as the fluid gets absorbed by the lining of the abdominal cavity.”