What causes endometriosis?

The exact cause of endometriosis is unknown. But possible explanations for how it develops include:

  • Retrograde menstruation. In retrograde menstruation, menstrual blood containing endometrial cells flows back through the fallopian tubes and into the pelvic cavity instead of out of the body. These displaced endometrial cells stick to the pelvic walls and surfaces of pelvic organs, where they grow and continue to thicken and bleed over the course of each menstrual cycle.
  • Transformation of peritoneal cells. In what's known as the "induction theory," experts propose that hormones or immune factors promote transformation of the cells that line the inner side of your belly (peritoneal cells) into endometrial cells.
  • Embryonic cell transformation. Hormones such as estrogen may transform cells in the earliest stages of development (embryonic cells) into endometrial cell implants during puberty.
  • Surgical scar implantation. After a surgery, such as a hysterectomy or C-section, endometrial cells may attach to a surgical incision.
  • Endometrial cell transport. The blood vessels or tissue fluid (lymphatic) system may transport endometrial cells to other parts of the body.
  • Immune system disorder. A problem with the immune system may make the body unable to recognize and destroy endometrial tissue that's growing outside the uterus.

Endometriosis can cause pain — sometimes severe — especially during menstrual periods. It can also cause fertility problems. But effective treatments are available. See your doctor if you have painful menstrual periods or trouble getting pregnant.


Tatnai Burnett, M.D.

March 28, 2019 See more Expert Answers