There are a few known cases of people getting HIV from giving oral sex (licking or sucking). There are no known cases of someone getting HIV from receiving oral sex (being licked or sucked). Experts believe that oral sex without protection is less risky than other kinds of sex, but all agree that it is possible to get HIV from giving oral sex to an HIV-infected partner without protection, especially if the HIV-infected partner ejaculates in the mouth. Certain factors, such as the presence of any cuts or sores in the mouth, are thought to increase the riskiness of oral sex.
Giving oral sex (blow job) to a man has been proven to carry some risk of getting HIV, although most scientists believe the risk is relatively low. The risk increases if the person giving the blow job has any cuts or scrapes in his or her mouth, even small ones that can be caused by brushing or flossing right before sex. To have safer oral sex, avoid getting any semen in your mouth, either by pulling away before ejaculation, or by using a nonspermicidal condom. You can use an oral barrier such as a dental dam or plastic wrap to make oral-anal sex (rimming) safer.
Giving oral sex to (going down on) a woman is also relatively low risk. The possibility of infection is higher if there is menstrual blood or if the woman has another STD. You can use an oral barrier such as a dental dam or plastic wrap to make oral-vaginal sex (cunnilingus) or oral-anal sex (rimming) safer.
There are many diseases besides HIV that can be passed through unprotected oral sex, including herpes, syphilis, gonorrhea, hepatitis A, warts, intestinal parasites, and others.