You can’t have intercourse until 24 hours after your period has cleared. Because the menstrual period is not completely clean, if intercourse may cause the backflow of menstrual blood, or endometrial inflammation, because at this time the cervical mucus plug has not yet formed, if intercourse may cause bacterial infection, as well as endometrial inflammation, serious cases will cause tubal blockage and pelvic inflammatory disease. It is also possible for menstrual blood to enter the abdominal cavity along both fallopian tubes, because this blood contains a large amount of endometrium, so it may cause endometriosis and adenomyosis, and infertility, so it is not possible to have intercourse before menstruation is clean.