There is practically no possibility of contract any STD by kissing. There is no known case of a HIV infection contracted by kissing. This, however, does not mean that the HIV virus cannot be found in saliva. It is present, but in small quantities. Nevertheless, some care should be taken, especially if one of the partners has bleeding ulcers in his or her mouth. In this case, HIV infection is at least theoretically possible.

Kissing brings the risk of infection with Hepatitis B virus and with the agent of syphilis (Treponema pallidum). These two viruses may be present in small wounds in the mouth and mucous membrane of the oral cavity. There is a possibility of infection with the herpes virus (HSV), too. In the event that one of the partners is infected and has herpetic blisters on his or her lips, the probability of infection is very high. An infection with a herpes virus (HSV) is possible also when there are no symptoms of this disease.