Oral sex can transmit at least six major sexually transmitted infections: chlamydia, gonorrhea, syphilis, herpes, HPV, and HIV. Oral-anal contact adds hepatitis A, hepatitis B, and intestinal parasites to that list. The risk level varies significantly by infection, and many oral STIs produce no symptoms at all, which makes them easy to spread without knowing.
Gonorrhea and Chlamydia in the Throat
Gonorrhea is one of the most easily transmitted STIs through oral sex, particularly when performing oral sex on a penis. The bacteria readily infects the throat, causing what’s known as pharyngeal gonorrhea. In studies of men who have sex with men, pharyngeal gonorrhea was found in about 4.6% of those tested, while pharyngeal chlamydia showed up in about 1.4%.
The tricky part: throat infections with either of these bacteria are usually asymptomatic. You won’t get the obvious burning or discharge that genital infections cause. Most people have no idea they’re carrying the infection in their throat, which means they can pass it to a partner’s genitals during oral sex without any warning signs. This silent reservoir is a major reason these infections keep circulating.
If you’re sexually active and have oral sex, standard genital testing won’t catch a throat infection. You need a specific throat swab. The FDA has cleared nucleic acid tests (the Aptima Combo 2 and Xpert CT/NG) specifically for detecting chlamydia and gonorrhea at throat and rectal sites. Current guidelines recommend that men who have sex with men get screened at least annually at all sites of contact, including the throat, regardless of condom use. For women and other groups, throat screening is based on sexual history and a conversation with your provider.
Herpes: The Cold Sore Connection
Herpes simplex virus type 1, the virus behind cold sores, is one of the most common infections spread through oral sex. When someone with HSV-1 on their mouth performs oral sex, they can transmit the virus to their partner’s genitals. This is now a leading cause of genital herpes cases.
What makes herpes particularly easy to transmit is viral shedding. The skin can release the virus even when no visible sore is present, which means someone can pass it along without any active outbreak. You can also get genital herpes from a partner who doesn’t know they’re infected. Condoms reduce the risk but don’t eliminate it, because the virus can shed from skin areas a condom doesn’t cover.
HSV-2, the type more commonly associated with genital herpes, can also spread to the mouth through oral sex, though this happens less frequently than HSV-1 traveling in the other direction.
HPV and Oral Cancer Risk
Human papillomavirus spreads easily through oral sex and is now the dominant cause of oropharyngeal cancers (cancers of the back of the throat, base of the tongue, and tonsils). HPV is thought to cause 60% to 70% of these cancers in the United States.
Most oral HPV infections clear on their own and never cause problems. But in a small percentage of people, high-risk strains persist and can, over years or decades, lead to cancer. The risk is higher with more oral sex partners over a lifetime. The HPV vaccine protects against the strains responsible for these cancers, which is one reason vaccination is recommended for everyone through age 26, and in some cases up to 45.
Syphilis Through Oral Contact
Syphilis spreads through direct contact with a syphilis sore, and those sores can appear on or around the lips, inside the mouth, or on the tongue. During the primary stage, the sore is typically firm, round, and painless, which means you might not notice it on a partner or even on yourself. During the secondary stage, sores can appear in the mouth as well.
Because transmission requires contact with a sore, condoms help only if they cover the sore. If a syphilis lesion is on the lips or another uncovered area, contact can still transmit the infection. Syphilis rates have been climbing in recent years, making this a more relevant concern than it was a decade ago.
HIV: Very Low but Not Zero
HIV transmission through oral sex is technically possible but carries extremely low risk compared to vaginal or anal sex. The CDC categorizes oral sex as having “extremely low to no HIV risk.” The chance increases if there are open sores, cuts in the mouth, bleeding gums, or if the person giving oral sex has recently had dental work. For most people, oral sex is not a meaningful route of HIV transmission.
Risks Specific to Oral-Anal Contact
Oral-anal sex (rimming) introduces a different set of infections because it involves the fecal-oral route. Hepatitis A and hepatitis B can both spread this way. Intestinal parasites, including Giardia, are also a real concern. One study of men who have sex with men presenting with gastrointestinal symptoms found Giardia in 11% of patients. Bacteria like E. coli and Shigella can spread through oral-anal contact as well.
Giardia in particular causes inflammation of the small intestine, leading to diarrhea, cramping, bloating, and nausea that can last weeks if untreated. These infections are often grouped under “enteric STIs” and can be misdiagnosed as food poisoning or a stomach bug if you don’t mention your sexual history to a provider. Hepatitis A vaccination is an effective preventive measure, and it’s recommended for men who have sex with men and others at elevated risk.
How to Reduce Your Risk
Condoms (for oral sex on a penis) and dental dams (for oral sex on a vulva or anus) create a physical barrier between the mouth and a partner’s skin or mucous membranes. Condoms have strong evidence for reducing STI transmission. Dental dams are widely recommended based on the same logic, though direct research on their effectiveness is limited, partly because so few people use them consistently and study sizes have been small.
Beyond barriers, a few practical steps lower your risk. Getting tested regularly, including throat swabs if you have oral sex, catches infections that produce no symptoms. The HPV vaccine prevents the strains most likely to cause cancer. Hepatitis A and B vaccines protect against those specific infections. Avoiding oral sex when you or a partner has a visible sore, cut, or bleeding gums also reduces transmission of several infections on this list.
If you’re getting tested, be specific with your provider about the types of sex you have. A standard STI panel tests urine or genital swabs, which will miss a throat or rectal infection entirely. Asking for site-specific testing is the only way to get a complete picture.