The exact causes that trigger the disease remain unknown. Various accepted theories have tried to find an explanation, the most prominent ones are:
The implantation theory (Sampson theory). According to this theory, endometriosis occurs because part of the menstrual tissue migrates back up the Fallopian tubes and accumulates on the pelvic organs, instead of flowing out of the vagina as it does during normal menstruation. This theory provides the best explanation for most cases, as 90% of women present retrograde menstruation.
The induction theory. In this theory, endometriosis results from the differentiation of mesenchymal cells found in the connective tissue; these cells are activated by substances that release degenerated endometrium and eventually reach the abdominal cavity.
In situ development theory. This theory is based on the idea that ectopic endometrium develops in situ from local tissues and pluripotent cells found in the surface of the peritoneum. This hypothesis is best used to explain cases of endometriosis in atypical locations.
Risk factors associated with endometriosis
Included among the risk factors that could be related to the development of endometriosis are:
Early onset of menstruation (menarche). Before 11–13 years.
Short menstrual cycle. High frequency periods (less than 28 days from the start of bleeding until the next bleeding event).
Heavy bleeding or which lasts for several days.
Late first pregnancy or never having been pregnant.
Surgical interventions that affect the uterus, such as uterus scraping or a caesarean delivery. The disease is more frequent in white women (but this might just be because it is underdiagnosed in black women who form the majority in underdeveloped countries).
First-degree relatives diagnosed with endometriosis. A hereditary element may exist in up to 10% of cases. It is a probably a disease that follows a multifactorial/polygenic inheritance.
Environmental factors. These are associated with toxic agents that act as endocrine disruptors.
Despite being considered a primarily hormonal disorder, some women are more likely to develop endometriosis than others due to genetic, immunological and environmental factors.