The exact cause of endometriosis is not known, but researchers have some theories.
It may result from something called "retrograde menstrual flow," in which some of the tissue that a woman sheds during her period flows through her fallopian tubes into her pelvis. While most women have some retrograde menstrual flow during their periods, not all of these women have endometriosis. Researchers are trying to uncover what other factors might cause the tissue to attach and grow in some women, but not in others.1,2
Researchers believe that endometriosis likely results from a combination of factors, including (but not limited to) some of the following:
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