Health on care :As seen in the definition of endometriosis, the cause of the disease is poorly understood (but read the last paragraph under causes endometriosis).

It is possible that fragments are improperly disposed of uterus during menstruation. These fragments then go back into the tubes and would set in different organs by forming cysts: 

 

• on the uterine muscle (case of adenomyoma)
• on the ovary
• on the peritoneum and the intestine (more rarely)

 

These fragments, like the endometrium, respond to hormonal changes of the female body. They grow under the action of estrogen and progesterone, and then bleed when hormone levels fall, during menstruation. This explains heavier bleeding experienced by women, when it is suffering from endometriosis.

But these fragments can take as badly (as they are outside the womb), then they can irritate and cause pain. See part symptoms of endometriosis

It is however certain that these fragments of uterine tissue reacts to estrogen. Out, this rate is especially important between 25 and 40. This is why women of this age are prone to endometriosis. This rate lowering during menopause, the disease tends to be reabsorbed. That is why there are different strategies of treatment of endometriosis. See section treatment of endometriosis