Endometriosis is a disease characterized by the growth of tissue resembling the endometrium, or lining of the uterus, in other areas of the body, usually in the pelvic region. These growths swell and shed with the menstrual cycle just like the normal endometrium, but because they are not in the uterus, they cannot be expelled. This results in pain, inflammation, and infertility.

The exact cause of endometriosis is not well understood, and it is likely that a combination of factors is responsible for the development of the disease. Hormonal factors seem to play an important role in the disease’s development.

The female hormonal cycle

The lining of the uterus changes throughout a woman’s monthly cycle in response to hormones. In the first part of the cycle, estrogen levels are high and cause the endometrium to grow and thicken in preparation for a potential pregnancy. Once an egg is released from the ovaries, the levels of another hormone called progesterone start to increase to further prepare the endometrium for a potential pregnancy. If no pregnancy occurs, the levels of estrogen and progesterone drop, triggering a woman’s period.

Estrogen and endometriosis

Because endometrial lesions are responding to changes in the levels of estrogen, like the normal endometrium, some endometriosis treatments are aimed at reducing or blocking estrogen secretion.

A further piece of evidence that strongly suggests that estrogen is implicated in the development of endometriosis is the fact that rare cases of endometriosis have been reported in men taking estrogen as a hormonal supplement.

Metaplasia, when cells outside the uterus change to become endometrial, has been suggested as a possible cause of endometriosis. Some researchers have suggested that hormone changes might trigger metaplasia and the conversion of different cell types into endometrial cells.

Interaction of estrogen with other endometriosis risk factors 

Environmental factors can affect estrogen levels and therefore indirectly trigger the development of endometriosis.

Genetic factors may also predispose some women to developing endometriosis by influencing the amount of estrogen they produce.


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