You should never have intercourse during menstruation, even with a condom. Because the endometrium is shed during menstruation, there will be trauma formation in the uterine cavity, and the immunity of the body decreases during menstruation, which may cause bacterial infection and may form endometritis, adnexitis or pelvic inflammatory disease. If there is severe endometritis, adnexitis or pelvic inflammatory disease, it may affect future pregnancy. In addition, sexual excitement in women may cause menstrual blood to flow backwards and cause endometriosis. If there is endometriosis, progressive aggravation of menstrual pain can occur and it may affect future pregnancy, so it is important to avoid having sex during menstruation.