Endometriosis refers to the condition where active endometrial cells implant outside the uterine lining. It is a relatively common gynecological disease. Pain usually begins one to two days before menstruation starts, is most severe on the first day of menstruation, and gradually lessens thereafter. The pain generally persists throughout the menstrual period. It is advised that patients with endometriosis seek timely treatment under the guidance of a clinical doctor, based on their individual conditions, to prevent the progression of the disease and serious health consequences.