Endometriosis is a disease – often progressive – in which islands of the mucous membrane lining the uterus implant themselves outside the uterus. Endometriosis sites are most often located in the lower abdomen (for example on the peritoneum, in the ovaries, bowel or bladder); less commonly these sites can also be found in other organs (skin, lungs). Endometriosis sites are subject to the influence of the hormones that control the menstrual cycle. In the same way as the normal uterine mucosa – also known as the “endometrium” – endometriosis sites follow a cyclic pattern as they develop and bleed.

It is still not known why endometriosis develops. The risk is increased when a woman’s periods are prolonged or her cycles are shortened. However, there are also genetic factors and toxic environmental factors, such as dioxin, which predispose certain women to endometriosis.

The term “retrograde menstruation” means that, during periods, part of the menstrual blood flows into the abdominal cavity via the fallopian tubes. This phenomenon plays an important role in the development of endometriosis. This blood actually contains endometrial cells that are viable. If the mucous membrane presents increased resistance or if the women suffers from a certain weakness of the immune system, the mucosal cells may survive in the abdominal cavity and adhere to the peritoneum or even become implanted there.