There is a type of tissue that is found in the lining of the uterus called the endometrium. There are cases where this tissue also develops on the outside of the uterus, this is a condition known as endometriosis.
The menstrual cycle is about twenty eight days long and typically the endometrium goes through a number of changes afterwards. In preparation for pregnancy, the endometrium develops and thickens. You can get information about the most common endometriosis symptoms via https://endometriosisassn.org/about-endometriosis/endometriosis-symptoms.
Endometrial tissue develops on the outside of the uterus still behaves as if it was inside the uterus. In rare instances, the endometrial tissue may develop in other areas of the body. When the endometrial tissue grows in the ovary, it can lead to a cysts, this is known as endometrioma.
There isn't a clear cause of endometriosis. During the menstrual period there is a small amount of blood cells that flow from the fallopian tubes to the abdomen instead of flowing out. In a woman that has endometriosis these cells stick to the pathway areas and start to grow.
Women at Risk
The majority of women that have this condition are between the ages of 30 and 40. This doesn't mean women outside of this age group aren't affected; endometriosis can affect any female that menstruates. Those that menstruate but never have a child are more commonly affected by this condition. It has also been noted that family history plays a role in development of endometriosis.