Endometriosis is a common fertility problem that women can experience during their childbearing years. It occurs when the type of tissue that lines your uterus is also growing outside of your uterus. This extra tissue does not always cause noticeable symptoms and it usually isn’t dangerous, but it can cause pain and other problems.
The clumps of tissue that grow outside your uterus are called implants. Implants usually grow on the ovaries, the fallopian tubes, the outer wall of the uterus, the intestines, or other organs in the belly. In rare cases, these tissues spread to areas beyond the belly.
Currently, there is no known cause of endometriosis. Researchers suggest that one possible cause could be “reverse menstruation,” or a phenomenon where the tissue shed during menstruation backs upward through the fallopian tubes and begins growing into the abdomen. Other theories suggest that the condition is related to immune system disorders or the transformation of peritoneal cells.