Sexual intercourse is not allowed when menstruation is not completely clean. First of all, menstruation is a stage of lower resistance. When you have menstruation, the mouth of the uterus is open, and bacteria are easy to enter the uterine cavity through the open mouth, which will increase the probability of endometritis, cervicitis, and endometriosis occurring, which will have an impact on the health of women. Secondly, during the menstrual period, menstrual blood will also have an effect on the male genitals, and some men may experience itching, redness and swelling of the genitals after having sex during the menstrual period, which can also easily lead to the occurrence of some diseases, so be sure to have sex after the menstrual period is completely clean.