The most widely accepted theory is retrograde menstruation. According to this theory some of the menstrual blood flows backwards down the fallopian tubes and into the pelvis. Some of the endometrial cells, contained in the menstrual fluid, implant on the reproductive organs or other areas in the pelvis. These implanted cells cause endometriosis. What is not known is why these endometrial cells implant in some women and not in others.
Other theories are:
- Lymphatic or circulatory spread
- Genetic predisposition to the condition
- Immune dysfunction
- Environmental causes - such as dioxin exposure