Normally, women shed their endometrium every month, causing the capillaries to rupture and bleed, and the blood, mixed with the shed endometrium, is discharged from the vagina. However, in some women, due to certain factors, menstrual blood is not discharged from the vagina, but flows from the vagina back to the uterus and through the fallopian tubes to the abdominal cavity, etc. This is called menstrual blood reflux. If the amount of refluxed menstrual blood is relatively small, it usually has no adverse effects and will be gradually absorbed by the abdominal cavity lining. If menstrual reflux occurs regularly and the amount of refluxed blood is relatively large, the menstrual blood cannot be completely absorbed in the abdominal cavity and may easily form a mass in the pelvic cavity. Menstrual blood reflux also tends to bring endometrial fragments to the abdominal cavity and ovaries and other parts of the body, leading to endometriosis, causing more serious symptoms such as menstrual pain, and in some cases, endometriosis to the muscular layer, forming adenomyosis, which affects women’s health.