Frequent licking of the nipples does not usually cause oral disease. Licking the nipple is a foreplay in normal intercourse activities and this act does not cause oral diseases and other after-effects. If it is simply oral contact does not lead to the spread of disease, especially the more concerned about sexually transmitted diseases, and does not spread through the sucking of female breasts. However, if the nipple is ruptured or broken due to excessive force or biting with teeth during licking and sucking, the bacteria in the mouth will probably cause nipple infection, which may induce mastitis in severe cases.