Women can never have sex during menstruation. The immunity of women during menstruation is relatively low, and if they have sex during menstruation, retrograde infections may occur. Because the cervix is in a slightly open state during menstruation, it is easy to be infected by bacteria, bacteria can enter the uterus through the cervical canal during coitus, causing endometritis, adnexitis, the infection can spread to the pelvic cavity and cause pelvic inflammatory disease, the woman may be more emotional during menstruation, the uterus will be congested in a large number of coitus, and the uterus will undergo irregular contractions after coitus, resulting in a large number of bleeding caused by anemia. The pressure on the abdomen may increase during menstruation, and the backflow of menstrual blood may cause endometriosis, adenomyosis, and ovarian chocolate cysts, accompanied by severe menstrual cramps, which may affect fertility in the future.