Oral-anal contact (rimming) carries real infection risks, but they can be significantly reduced with the right precautions. The main concern isn’t STIs in the traditional sense, though those are possible too. The bigger and more common risk is swallowing bacteria and parasites found in fecal matter, even in trace amounts invisible to the eye.
Why the Risks Are Different From Other Oral Sex
The anus is the exit point for the digestive tract, which means the surrounding skin can harbor bacteria and parasites regardless of how clean it looks. Oral-anal contact creates a direct fecal-oral route, the same transmission pathway responsible for food poisoning and waterborne illness. The difference is that the exposure happens during sex rather than from contaminated water or food.
A large cross-sectional study at a major UK sexual health clinic found that roughly 1 in 10 participants tested positive for at least one bacterial gut pathogen. The most common was a strain of E. coli (enteroaggregative E. coli) detected in about 5% of those tested, followed by Campylobacter and enteropathogenic E. coli at around 1.7% each. Shigella, a particularly unpleasant bacteria that causes severe diarrhea and cramps, showed up in just under 1%. These pathogens were present in people who had no symptoms, meaning a partner can carry and transmit them without knowing.
Gut Infections: The Most Common Risk
The infections most strongly linked to oral-anal contact are gastrointestinal, not genital. Shigella is one of the best-documented examples. It spreads extremely easily because it takes only a tiny number of bacteria to cause illness. Symptoms typically include watery or bloody diarrhea, stomach cramps, and fever. The CDC specifically flags sexual activity, including mouth-to-anus contact, as a transmission route and notes that the bacteria can be present on skin around the anus, thighs, and buttocks even after washing.
Parasites are the other major category. Giardia, which causes bloating, nausea, and prolonged watery diarrhea, transmits exclusively through the fecal-oral route. Studies have found prevalence rates of 4 to 18% in sexually active male populations where oral-anal contact is common, well above background rates. Entamoeba histolytica, the parasite that causes amebiasis (potentially severe intestinal and liver infection), follows the same transmission path and has been called the most common intestinal parasite seen in communities where anal-oral sexual practices are frequent.
These gut infections range from mild and self-limiting to seriously debilitating. Giardia can cause weeks of digestive problems. Amebiasis can, in rare cases, spread to the liver. Shigella is increasingly antibiotic-resistant, making treatment harder.
STIs and Hepatitis
Beyond gut pathogens, oral-anal contact can transmit several sexually transmitted infections. The CDC lists chlamydia, gonorrhea, syphilis, herpes (both types), HPV, and HIV as infections that can spread through oral sex, including anilingus specifically. Herpes sores around the mouth or anus make transmission straightforward. HPV is particularly relevant because certain strains transmitted to the mouth and throat can, over time, develop into oral or neck cancers.
Hepatitis A is one of the most significant risks specific to oral-anal contact. During a hepatitis A outbreak in Krakow, Poland, 71% of cases were traced to oral-anal sexual contact. Hepatitis A causes weeks of fatigue, nausea, jaundice, and liver inflammation. While it usually resolves on its own, it can be severe enough to require hospitalization. Hepatitis B can also spread through this route.
How to Reduce the Risks
No method eliminates risk entirely, but several strategies lower it substantially.
Dental dams are thin sheets of latex or polyurethane placed over the anus during oral contact. They create a physical barrier between the mouth and skin. While there isn’t enough research to put a precise number on how much they reduce transmission, the logic is the same as condoms: a barrier prevents direct contact with infectious material. Condoms have repeatedly been shown to reduce STI risk, and experts generally extrapolate similar protection to dental dams when used correctly. You can also cut a condom lengthwise to create an improvised dam if you don’t have one.
Washing beforehand helps reduce the bacterial load on the skin. A shower with warm water immediately before is the standard recommendation. Avoid using soap directly on the anus, as it’s sensitive tissue and irritation can actually create micro-abrasions that increase infection risk. The goal is to remove visible matter and surface bacteria, not to sterilize the area (which isn’t possible).
Avoid brushing your teeth right before or after. Brushing creates tiny cuts in your gums that give bacteria and viruses a direct entry point into your bloodstream. If you want a clean mouth beforehand, rinse with mouthwash instead, and wait at least an hour after brushing before any oral-anal contact.
Don’t move from anus to mouth to genitals without cleaning in between. Indirect transmission happens when bacteria from the anus reach the mouth, genitals, or hands and then get transferred further. Washing hands and changing barriers between activities breaks that chain.
Vaccines That Protect You
Vaccination is one of the most effective tools available. The CDC recommends hepatitis A and hepatitis B vaccines for anyone who is sexually active with more than one partner, and specifically for men who have sex with men. If you engage in oral-anal contact with any regularity, getting vaccinated against both forms of hepatitis is a straightforward way to remove two of the more serious risks from the equation entirely.
HPV vaccination is recommended for everyone through age 26 and is available through age 45 for those who haven’t been vaccinated. Since HPV transmitted to the throat can eventually cause cancer, this vaccine offers meaningful long-term protection for anyone engaging in oral sex of any kind.
Signs Something Was Transmitted
Gut infections from oral-anal contact typically show up within one to three days for bacterial pathogens like Shigella, or one to two weeks for parasites like Giardia. Watch for watery or bloody diarrhea, persistent stomach cramps, nausea, or fever that develops within a few weeks of sexual contact. These symptoms are often mistaken for food poisoning, and many people never connect them to sexual activity, which means they go untreated and can be passed to others.
Hepatitis A has a longer incubation period, typically two to four weeks, and announces itself with fatigue, loss of appetite, nausea, and sometimes yellowing of the skin or eyes. Herpes and syphilis sores around the mouth may appear within a few days to a few weeks. If you develop any of these symptoms after oral-anal contact, let your healthcare provider know the specific sexual activity involved so they can test for the right infections. Many of these pathogens won’t show up on a standard STI panel unless specifically requested.