The serious consequences of having intercourse during menstruation are the following: First, it is easy to cause gynecological inflammation in women because the endometrium is shed during menstruation, and the endometrium acts as a barrier to women, blocking external bacterial infections. When having intercourse during menstruation, women are likely to contract gynecological infections, such as vaginitis, uterine infections and adnexitis, because men carry germs and transmit them to women. These inflammations can spread and even lead to peritonitis, and may cause infertility. Secondly, it may cause women to have more bleeding, because during menstruation the endometrium is the period of shedding, when it is more brittle and thinner, when intercourse is likely to lead to rupture of small blood vessels in the uterus, bleeding, resulting in more blood loss in women.