This is possible, but not very common. If your partner's mouth is infected with an STI, then he or she may be able to pass that infection to your mouth during a kiss. Fever blisters and cold sores can be passed through a kiss if your partner is infected. Blood-borne infections like HIV or Hepatitis B or C can only be passed through kissing if there is an exchange of infected blood. If your partner has an infection in his or her genital area, then kissing on the mouth will not transmit the infection. However kissing the infected area may lead to transmission of the infection.