It is not allowed to have sex during menstruation. The endometrium is shed during menstruation and the blood sinuses inside the uterine cavity are open and there are small blood clots, which is very suitable for the growth of bacteria. Having sex during menstruation gives a good opportunity for bacteria to grow and infect the body, leading to a series of negative consequences later on. The hazards of menstrual intercourse are very great: one, easy to cause various inflammatory diseases, such as endometritis, tubitis, pelvic inflammatory disease, can also lead to late infertility probability increased. Second, menstrual intercourse can cause uterine contraction, so that menstrual blood into the abdominal cavity, the risk of causing endometriosis. Some sperm and other components of semen may enter the blood circulation of women through small blood vessel fissures during menstrual intercourse, stimulating the immune system and forming anti-sperm antibodies, causing immune infertility. Fourth, various blood-borne infections can spread to each other. V. Intercourse during menstruation can cause increased bleeding or prolonged bleeding, resulting in late menstrual irregularities.