You should not have intercourse on the first day of your period, regardless of the first day of your period. The onset of menstruation represents the opening of the uterine opening and the beginning of shedding of the endometrium, where traumatic surfaces are formed. During menstruation, women’s immunity decreases and the vagina becomes less clean. If sexual intercourse occurs at this time, male genitalia can bring germs into the vagina and enter the uterine cavity by the way and infection can easily occur. For example, endometrial inflammation, tubal inflammation, etc., and even cause infertility. At the same time, sexual intercourse will make the menstrual blood flow backwards, and may also cause endometriosis, and the prostaglandins carried by male ejaculation will cause dysmenorrhea, with serious consequences, so the entire menstrual period should not have intercourse. The woman should pay attention to warmth during the menstrual period, eat less cold, keep a happy mood, change sanitary napkins and underwear, rinse the private parts with warm water and pay attention to the hygiene of the private parts.