No one knows exactly what causes endometriosis, but over the years many theories have been advanced.
Endometriosis affects 90 million women worldwide and about 12 million in the United States.

The uterus is an organ that has thick, muscular walls. The inner lining is called the endometrium. In the first part of the menstrual cycle, the hormone called estrogen causes this lining to become thickened and engorged. This is in preparation for the fertilization of the egg If the egg is not fertilized, a hormone called prostaglandin causes the thickened lining to be peeled away. Normally this is pushed out if the uterus and expelled through the vagina. This is menstruation. In endometriosis, cells of the endometrium end up on other organs outside of the uterus. In some cases this happens because the menstrual flow backs up through the fallopian tubes and spills into the abdominal cavity. The endometrim cells then attach onto organs outside of the uterus. These organs include the ovaries, the bladder, the kidneys, the bowels and even the lungs in rare cases. These endometrial cells then form lesions or growths on these organs. The lesions still respond to prostaglandin and this will cause them to build up, break down and bleed every month. The problem is that this blood had nowhere to go and stays within the abdomen. Besides bleeding, this trapped endometrial tissue can also cause organ inflammation, formation of scar tissue and above all, intense pain. Some women suffer from stretched out tissue or adhesions. During menstruation, blood leaks from the endometrial lesions that are attached to pelvic organs. The blood acts like toffee attaching itself to two or more organs and pulling them together.
Women with endometriosis can also develop chocolate cysts on the ovaries. These cysts are filled with blood and mucus and sometimes rupture. A ruptured cyst is intensely painful and can spread endometriosis to new areas. Woman with endometriosis may have one, some or all of these symptoms: pain before and during periods, pain during and after sex, infertility, fatigue, painful urination during periods, painful bowel movements during periods and other gastrointestinal upsets such as diarrhea, constipation and nausea. The only way to confirm a diagnosis of endometriosis is by a surgical procedure known as laparoscopy.

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