The first is that when a woman is on her period, the cervix is open and the endometrium is bleeding and the blood is a breeding ground for bacteria, which can easily lead to bacterial infection of the reproductive tract and can trigger pelvic inflammatory disease and vaginitis. Secondly, when women have intercourse during menstruation, the uterus will contract due to excitement, menstrual blood will reflux, menstrual blood will also increase, which will prolong the period, and in serious cases, because of intercourse during menstruation, endometriosis will be triggered, women will have dysmenorrhea, and even lead to infertility. Thirdly, having intercourse during menstruation is also very bad for men, and can easily cause male urethritis due to stimulation by menstrual blood. So women are not finished with their periods, it is best not to have intercourse, it is recommended to have intercourse after three days of clean menstruation, and theoretically in these three days is not easy to get pregnant, belongs to the safe period.