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By Mayo Clinic staffThe cause of endometriosis remains uncertain. Experts are studying the roles that hormones and the immune system play in this condition.
One theory holds that menstrual blood containing endometrial cells flows back through the fallopian tubes, takes root and grows. Another hypothesis proposes that the bloodstream carries endometrial cells to other sites in the body. Still another theory speculates that a predisposition toward endometriosis may be carried in the genes of certain families. A faulty immune response also may contribute to the development of endometriosis.
Other researchers believe that certain cells present within the abdomen in some women retain their ability to become endometrial cells. These same cells were responsible for the growth of the women's reproductive organs at the embryo stage. It's believed that genetic or environmental influences in later life allow these cells to give rise to endometrial tissue outside the uterus.