Under normal circumstances, the endometrium grows inside the uterine cavity, but for various reasons, the endometrium may grow in any part of the body outside the uterine cavity, such as in the ovaries, abdominal cavity, etc. This phenomenon is called endometriosis. Normal endometrial cells should grow in the uterine cavity, but since the uterine cavity is connected to the pelvic cavity through the fallopian tubes, endometrial cells may enter the pelvic cavity through the fallopian tubes and grow ectopically in other areas, and the endometrium in the ectopic area will shed with the menstrual cycle, causing bleeding that can cause severe abdominal pain. Endometriosis may also cause adhesions in the fallopian tubes and failure of the fertilized egg to implant in the endometrium, which may lead to infertility. The causes of endometriosis are many, such as genetic factors, immune factors, and may be related to multiple abortions and induced abortions. Women with severe menstrual cramps should be highly suspicious of endometriosis and should go to the hospital in time to check whether they have endometriosis and get timely treatment after diagnosis.