Oral sex can transmit at least six major sexually transmitted infections: gonorrhea, chlamydia, syphilis, herpes, HPV, and HIV. Oral-anal contact adds hepatitis A, hepatitis B, and several intestinal infections to that list. The risk level varies significantly by infection, with some spreading easily through oral contact and others being rare but still possible.
Gonorrhea
Gonorrhea is one of the most efficiently transmitted STIs through oral sex, and throat infections are more common than many people realize. In studies of men who have sex with men, pharyngeal (throat) gonorrhea showed up in about 4.6% of those tested, making it more common in the throat than chlamydia is. The catch is that throat gonorrhea rarely causes symptoms. Most people with it have no sore throat, no visible signs, and no idea they’re infected. That makes it easy to pass along unknowingly.
You can get throat gonorrhea by performing oral sex on someone with a genital or anal infection. You can also get genital gonorrhea from receiving oral sex from someone with a throat infection. Without testing, throat gonorrhea can persist for weeks or months, silently acting as a reservoir that keeps the infection circulating. If you’re having oral sex with new or multiple partners, a throat swab is the only way to know your status, since a urine test or genital swab won’t detect a throat infection.
Chlamydia
Chlamydia can also infect the throat, though it’s less common there than gonorrhea. Studies found pharyngeal chlamydia in about 1.4% of men who have sex with men who were screened. Like gonorrhea, throat chlamydia is almost always asymptomatic. It spreads the same way: giving oral sex to someone with a genital infection, or receiving it from someone with a throat infection.
Standard chlamydia screening (a urine sample or genital swab) misses throat infections entirely. If oral sex is part of your routine, mention it when you’re getting tested so your provider can swab the right site.
Syphilis
Syphilis spreads through direct contact with a syphilis sore, called a chancre. These sores can appear on the lips, tongue, gums, palate, or tonsils, and they show up 3 to 90 days after exposure. A chancre is typically a firm, painless, round ulcer, which makes it easy to overlook, especially when it’s tucked inside the mouth. It heals on its own after a few weeks even without treatment, but the infection doesn’t go away.
If primary syphilis goes untreated, it progresses to a secondary stage about 3 to 12 weeks after the sore resolves. At that point, symptoms can include a rash, sore throat, swollen lymph nodes, muscle aches, and headaches. The infection then enters a latent phase with no symptoms at all, which can last years or even a lifetime. In roughly one-third of untreated cases, it eventually reaches a tertiary stage that can damage the heart, brain, and other organs. Inside the mouth, advanced syphilis can destroy tissue in the palate badly enough to create a perforation.
Oral syphilis lesions most often appear on the sides and underside of the tongue, the gums, the hard and soft palate, and the lips. On the lips, they tend to look like ulcers with raised, firm borders. On the tongue, they may appear as whitish, striated patches surrounded by redness. Because these signs can mimic other conditions, syphilis is sometimes called “the great imitator,” and blood testing is the standard way to confirm it.
Herpes (HSV-1 and HSV-2)
Herpes is probably the most commonly transmitted infection through oral sex, largely because of HSV-1. Most people think of HSV-1 as “cold sores” and HSV-2 as “genital herpes,” but the reality is less tidy. HSV-1 can spread from the mouth to a partner’s genitals during oral sex, and this is now a leading cause of genital herpes in younger adults. HSV-2 can also spread from the genitals to a partner’s mouth, though this happens less frequently.
The virus sheds from the skin even when no sore is visible, which means transmission can happen at any time. Outbreaks tend to be less frequent when HSV-1 is in the genital area compared to the mouth, and less frequent when HSV-2 is in the mouth compared to the genitals. But the initial outbreak can still be painful regardless of location. There is no cure for herpes, though antiviral medication can reduce the frequency and severity of outbreaks and lower the chance of passing it on.
HPV and Oral Cancer Risk
Human papillomavirus spreads to the mouth and throat primarily through oral sex. Most oral HPV infections clear on their own and never cause problems. But certain high-risk strains can persist and, over years or decades, lead to cancer in the back of the throat, base of the tongue, or tonsils. HPV is now responsible for an estimated 60% to 70% of oropharyngeal cancers in the United States.
The HPV vaccine protects against the strains that cause these cancers. It’s most effective when given before someone becomes sexually active, but it’s approved for people up to age 45. If you were vaccinated as a teen, you likely already have protection against the highest-risk strains.
HIV
HIV transmission through oral sex is possible but extremely rare. A systematic review of transmission risk estimated that both giving and receiving oral sex carry a risk of 0 to 4 infections per 10,000 exposures. Researchers studying nearly 9,000 acts of receptive oral sex observed zero transmission events, though the sample wasn’t large enough to rule out a very small risk entirely.
Factors that could increase the already-low risk include having open sores or bleeding gums, other STIs present in the mouth or on the genitals, and exposure to ejaculate. For practical purposes, oral sex is considered a low-risk activity for HIV compared to vaginal or anal sex, but “low risk” is not the same as “no risk.”
Infections From Oral-Anal Contact
Oral-anal contact (rimming) opens the door to a different set of infections beyond the standard STI list. Hepatitis A is the most significant, spreading easily through fecal-oral contact even when hygiene seems adequate. During a hepatitis A outbreak among men who have sex with men in Krakow, Poland, 71% of cases were traced to sexual contact, with oral-anal sex reported by 68% of those infected. Hepatitis B can also spread through oral-anal contact.
Intestinal parasites like Giardia and bacteria like E. coli and Shigella can also be transmitted this way. These cause gastrointestinal symptoms ranging from mild diarrhea to severe cramping and bloody stool. A hepatitis A vaccine is available and highly effective, and it’s recommended for anyone at increased risk.
Why These Infections Get Missed
The biggest problem with STIs from oral sex isn’t that they’re hard to treat. It’s that they’re hard to detect. Most throat infections cause no symptoms, so people don’t seek testing. And standard STI panels typically screen only the genitals unless you specifically request throat or rectal swabs. A throat swab analyzed with a nucleic acid amplification test is the recommended method for detecting gonorrhea and chlamydia in the throat, though testing for gonorrhea at that site can sometimes produce false positives due to related bacteria that naturally live in the mouth.
If you’re having oral sex, the most useful thing you can do is tell your provider what kind of sex you’re having so they can test the right sites. Annual throat screening is recommended for men who have sex with men, but anyone having oral sex with new partners can benefit from site-specific testing.
Reducing Your Risk
Condoms (for oral sex on a penis) and dental dams (for oral sex on a vulva or anus) reduce direct skin-to-skin and fluid-to-mucous-membrane contact. They’re not perfect barriers against infections like herpes and HPV, which can spread from skin not covered by the barrier, but they meaningfully lower the odds of transmission for gonorrhea, chlamydia, syphilis, and HIV.
Vaccination covers two of the biggest long-term threats: the HPV vaccine protects against cancer-causing strains, and the hepatitis A and B vaccines protect against liver infections transmissible through oral-anal contact. Regular testing fills in the rest. Since most oral STIs are silent, screening at the correct body site is the only reliable way to catch them early and stop them from spreading.