ENDOMETRIOSIS CAUSES

Researchers aren't sure. Some physicians think a process called retrograde menstruation is to blame. The theory is that during your period, menstrual tissue flows backward through the fallopian tubes and into the abdomen, where it takes root and grows. Many researchers now believe, however, that all women experience some menstrual backup -- mostly without adverse consequences -- and that those who develop endometriosis must have a hormonal glitch or immune-system weakness that allows the tissue to become implanted. What's more, studies of sisters reveal that endometriosis appears to run in families, which points to a genetic link.

In rare cases, endometrial tissue can travel by way of the bloodstream or lymph nodes or can be spread during abdominal surgery. Some preliminary research suggests that the rise in the incidence of endometriosis may also be related to environmental toxins. One study of rhesus monkeys found that animals exposed to dioxin and PCBs developed spontaneous endometriosis. Researchers theorise that toxins like those trigger the disease by acting as hormone disrupters.