Causes of Endometriosis

Doctors do not know the exact cause for endometriosis. However, a number of theories have been developed to account for the presence of endometrial tissue outside of the uterus.

Retrograde menstruation – The most popular theory is that endometriosis results from menstrual blood and endometrial tissue that flows ‘backwards’, out of the fallopian tube and into the pelvis, rather than down through the cervix and out through the vagina. This is supported by the fact that endometrial implants are most often found on the ovaries, which are adjacent to the opening of the fallopian tubes. Endometriosis is also more common in young women with an obstruction (blockage) of the reproductive tract, which increases this retrograde flow of blood.3

Metaplasia – This theory suggests that endometrial implants arise from undifferentiated cells already lining the pelvic cavity. Undifferentiated cells are cells that have the ability to develop into multiple different tissues. The theory suggests that some precipitating event, possibly exposure to menstrual blood or changes in hormone levels, triggers these cells to develop into endometrial tissue.

Altered immunity – Women with endometriosis report higher rates of immune-mediated diseases including chronic fatigue syndrome, allergies and asthma.4   Deficiencies in the immune system could limit the body’s ability to recognize and eliminate abnormal implants of endometrial tissue outside of the uterus. Endometriosis is also associated with an increased number of certain subtypes of immune cells in the pelvic cavity; these cells release substances that encourage the growth of endometrial implants.5