The following are the main hazards: 1, women’s menstrual bleeding is actually endometrial bleeding, the uterus is very fragile, not only the lining of the trauma, and many blood vessels are exposed outside, if sexual relations is very easy to prolong the menstrual cycle, increasing female discomfort; 2, women’s immunity decreases during menstruation, the uterus self-defense function decreases, the cervical mouth is open, the uterus and vagina, sexual relations, once the male genitalia contain bacteria or suffer from hygiene diseases, it is easy to cause endometritis and pelvic infection. If you have sex, once the male genitalia contains bacteria, or suffer from unhygienic diseases, it is easy to cause infection in the uterus and pelvis, inducing endometritis, adnexitis, pelvic inflammatory disease and other gynecological diseases; 3, sex during menstruation when women are sexually excited, with the contraction of the uterus, it is easy to make the menstrual blood through the fallopian tube reflux to the pelvis, inducing endometriosis causing dysmenorrhea. In serious cases, it can also cause infertility.