Endometriosis is caused when cells that normally comprise the lining of the uterus (the endometrium) grow in other parts of a woman's body. These cells then bleed every time the woman has a menstrual period, and cause her internal organs to stick together with the blood and tissue that would normally be within the uterus.
The condition is usually found in women between the ages of 25 and 49, and is believed to affect up to 15 out of 100 women of child-bearing age. Endometriosis is most commonly found on the ovaries and Fallopian tubes, but it can also affect the tissues that secure the womb into place; as well as the bladder, bowel and other parts of the abdomen and pelvis.
Alongside painful and heavy periods, it can affect a woman's fertility if her ovaries, Fallopian tubes or uterus are damaged by the condition. Chronic abdominal pain, pain during sex and erratic periods are also classic symptoms.
While the exact cause is unknown, the risk of developing it increases if a woman started her periods early; has a mother or sister with the condition; or is experiencing a late menopause.
There is no cure for endometriosis, instead the condition must be managed. This includes the use of painkillers to tackle the discomfort; hormonal treatments to limit the size of the endometriosis; and surgery to remove as much endometriosis as possible.
Without treatment, some women may find that the condition resolves itself. However, in most cases, endometriosis will not clear until the menopause commences.