Causes of ovarian cysts 

Ovarian cysts often develop for no apparent reason in women who have monthly periods.

They can also affect women who no longer have periods, because they have been through the menopause.

Types of ovarian cyst

There are a many different types of ovarian cyst, which can be categorised as either "functional cysts" or "pathological cysts".

Functional cysts

Functional ovarian cysts form due to a minor problem in the menstrual cycle. They affect girls and women who have not been through the menopause, and are very common.

Each month, a woman's ovaries release an egg, which travels down the fallopian tubes into the womb (uterus), where it can be fertilised by a man's sperm.

Each egg forms inside the ovary in a structure known as a follicle. The follicle contains fluid that protects the egg as it grows and it bursts when the egg is released.

However, sometimes a follicle does not release an egg, or discharge its fluid and shrink after the egg is released. If this happens, the follicle can swell and become a cyst.

Functional cysts can also develop when the tissue left behind after an egg has been released (corpus luteum) fills with fluid.

Functional cysts are non-cancerous (benign) and are usually harmless, although they can sometimes cause symptoms such as pelvic pain. Most will disappear without treatment in a few months.

Pathological cysts

Pathological cysts are cysts caused by abnormal cell growth and aren't related to the menstrual cycle. They can develop before and after the menopause.

Pathological cysts develop from either the cells used to create eggs or the cells that cover the outer part of the ovary.

They can sometimes burst or grow very large and block the blood supply to the ovaries.

Pathological cysts are usually non-cancerous, but a small number are cancerous (malignant) and they are often surgically removed.

Conditions that cause ovarian cysts

In some cases, ovarian cysts are caused by certain conditions, such as endometriosis.

Endometriosis occurs when pieces of the tissue that line the womb (endometrium) are found outside the womb in the fallopian tubes, ovaries, bladder, bowel, vagina or rectum. Blood-filled cysts can sometimes form in this tissue.

Polycystic ovary syndrome (PCOS) is a condition that causes lots of small, harmless cysts to develop on your ovaries. The cysts are small egg follicles that do not grow to ovulation and are the result of altered hormone levels.

Page last reviewed: 09/12/2014

Next review due: 09/12/2016