Receptive anal sex carries the highest per-act risk of HIV among common sexual activities: roughly 138 per 10,000 exposures, or about 1 in 70, from a partner with untreated HIV CDC HIV estimates. The rectal lining is thin and tears easily. You can cut that risk dramatically with PrEP, condoms, a partner who's undetectable, and rectal STI testing.
Comparison
| Item | Per 10,000 exposures to a partner with HIV |
|---|---|
| Receptive anal | 138 |
| Needle-sharing | 63 |
| Insertive anal | 11 |
| Receptive vaginal | 8 |
| Insertive vaginal | 4 |
Why the rectal lining raises transmission risk
The rectum isn't built the way the vagina is. Its lining is a single, fragile layer of cells that absorbs fluid readily, that's its job, and it has no natural lubrication. During penetration it stretches and develops tiny tears you can't see or feel. Those microscopic breaks give viruses and bacteria a direct route into the bloodstream and to immune cells sitting just beneath the surface, which is exactly what HIV targets.
This is why being the receptive ("bottom") partner is consistently higher-risk than being the insertive partner across activities. For comparison, insertive anal sex runs about 11 per 10,000 exposures, receptive vaginal sex about 8, and insertive vaginal sex about 4. Oral sex carries a low HIV risk, and among non-sexual routes, sharing injection needles is high at about 63 per 10,000.
Use these numbers the way clinicians do: to rank activities so you spend your worry and your prevention where they count, not to call any single act "safe." These are averages per exposure, not guarantees: a single exposure can transmit HIV, and many exposures might not. Real risk also rides on your partner's viral load, whether either of you has another STI, and what prevention is in play. For the full head-to-head ranking, see our breakdown of std risk by sexual activity.
The STIs that matter most for receptive anal sex
Anything that lives in genital fluids or on skin can transmit through anal contact. Here's what's most relevant and what each one actually does.
HIV
HIV is the headline risk here because the rectal route is so efficient. Untreated, HIV gradually destroys the immune system, but with today's tools transmission is highly preventable, and a person living with HIV who's on treatment and undetectable does not pass it on through sex.
Gonorrhea and chlamydia
Gonorrhea and chlamydia both infect the rectum, often with no symptoms at all. When symptoms do show up, they look like proctitis: rectal pain, discharge, a feeling of needing to go, or bleeding. Untreated, these bacterial infections cause inflammation that can scar tissue and, importantly, raise your HIV risk by making the lining easier to breach.
Syphilis
Syphilis typically starts as a painless sore (a chancre) at the site of contact: which in receptive anal sex can be inside the anal canal, where you'd never notice it. Because it causes a break in the skin, having syphilis (or any sore-causing STI) raises HIV risk about 2.6 times, one more reason to test and treat early.
HPV
HPV (human papillomavirus) spreads through skin-to-skin contact and is extremely common. Most infections clear on their own, but certain strains cause anal warts, and high-risk strains can lead to anal precancer and cancer over years. The HPV vaccine prevents the strains responsible for most of those cancers.
Herpes
Herpes (HSV) causes painful blisters or ulcers around or inside the anus and sheds even when no sores are visible. Like syphilis, those breaks in the skin make HIV transmission easier, which is why herpes matters beyond the discomfort it causes.
Condoms and lubricant: getting it right for anal sex
Condoms cut HIV risk sharply and protect against the bacterial STIs that travel in fluid. The piece people get wrong is lube. Because the rectum makes none of its own, friction is what tears the lining: so generous lubricant isn't optional, it's part of the prevention.
- Use plenty of lube, reapply often, and choose water-based or silicone-based, these are safe with latex and polyisoprene condoms.
- Never use oil-based products (petroleum jelly, lotion, baby oil, coconut oil) with latex condoms: oil degrades latex and causes breakage; if you want oil-based lube, you'd need a non-latex condom.
- Put the condom on before any contact and use a fresh one if you switch from anal to vaginal or oral.
- Condoms and PrEP can be layered together for more protection than either alone.
PrEP for HIV prevention
PrEP (pre-exposure prophylaxis) is medication an HIV-negative person takes to block HIV before exposure, and it's the single most powerful tool for anyone who has receptive anal sex regularly. Taken consistently, PrEP cuts HIV risk by about 99%. It comes as a daily pill and, for some, a long-acting injection, and it requires routine check-ins with a clinician for HIV and kidney testing.
The reassuring math: the highest-risk activity also has the best protection. Between PrEP and a partner who's undetectable, the per-act numbers above stop being your reality. On the partner side, treatment is prevention, see how earlier hiv treatment can help prevention through viral suppression and U=U (undetectable equals untransmittable).
DoxyPEP to cut bacterial STI risk after sex
DoxyPEP is a dose of the antibiotic doxycycline taken after condomless sex to lower the chance of getting syphilis, chlamydia, and gonorrhea. Note the plural: it's an STI tool, not an HIV tool, and it does nothing against HIV or viral infections like herpes and HPV. Current guidance recommends it for specific groups at higher risk for bacterial STIs, including some men who have sex with men and transgender women. It pairs naturally with PrEP: PrEP covers HIV, DoxyPEP covers the bacterial STIs. Ask your clinician whether you're a candidate.
Rectal testing, don't rely on a urine test
A urine test only checks the urethra. If gonorrhea or chlamydia is sitting in your rectum, a urine sample misses it entirely. The right test is a rectal swab: a quick, simple swab of the anal canal that you can often self-collect. This is the most common mistake we see: people get a "full panel," come back negative, and never knew their highest-exposure site wasn't sampled. When you book, say plainly that you have receptive anal sex so the right sites get tested.
Routine testing for someone having receptive anal sex usually includes rectal gonorrhea and chlamydia, plus blood tests for HIV and syphilis. Timing matters, because each infection has its own detection window, here's when to test after exposure so you don't test too early. When you're ready, get tested at the right sites.
Vaccination: HPV and hepatitis B
Two vaccines belong in this conversation. The HPV vaccine prevents the strains that cause most anal cancers and warts, and it's recommended through adulthood for many people. The hepatitis B vaccine protects against a virus spread through sex and blood; if you're unvaccinated, this is a simple, durable layer of protection worth getting.
When to see a clinician
Book a visit if you have rectal pain, discharge, bleeding, sores, or a new bump, and don't wait for symptoms if you've had a higher-risk exposure. Same-day care matters in two situations: if you think you were exposed to HIV in the last few days, PEP (post-exposure prophylaxis) can still help but is time-sensitive; and if a sore or ulcer appears, get it checked promptly because syphilis and herpes are both treatable and both raise HIV risk.
Keep exploring on EasySTD: your risk of an STD, telling recent partners and HIV/AIDS testing.