Receptive anal sex carries the highest per-act HIV risk of any sexual activity — about 138 infections per 10,000 exposures, roughly 1 in 70, from a partner with untreated HIV CDC HIV estimates. The reason is anatomical: the rectal lining is thin and tears easily. It's also highly protectable with condoms, PrEP, and a partner who's undetectable.
| 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 |
How HIV and STI risk is measured
The CDC ranks sexual activities by the per-act risk of getting HIV from a partner who has HIV — with no condom, no PrEP, and no treatment in the picture — expressed as cases per 10,000 exposures. Framing it per 10,000 lets you put activities side by side and see which ones actually move the needle.
These are averages. A single exposure can transmit HIV, and many exposures might not. The real-world number for any one encounter swings on the partner's viral load, whether either person has another STI, and what prevention is being used. Use the figures to rank activities so you spend your worry — and your prevention dollars — where they count. For the full picture across every activity, see our guide to std risk by sexual activity.
The activities, ranked from highest to lowest risk
Here's how the common routes stack up per 10,000 exposures to a partner with untreated HIV. Being the receptive partner — the one being penetrated — is consistently higher-risk than being the insertive partner, across both anal and vaginal sex.
| Activity | HIV risk per 10,000 exposures |
|---|---|
| Receptive anal sex | About 138 (roughly 1 in 70) |
| Sharing injection needles (non-sexual) | About 63 |
| Insertive anal sex | About 11 |
| Receptive vaginal sex | About 8 |
| Insertive vaginal sex | About 4 |
| Oral sex | Low |
Receptive anal sex sits at the top by a wide margin, more than ten times the per-act risk of insertive anal sex and far above either direction of vaginal sex. Oral sex carries a low HIV risk. The needle-sharing figure is included as a yardstick: receptive anal sex is more than twice as risky per act.
Why the receptive partner faces higher risk
The rectum is built for absorption. Its lining is a single, thin layer of cells over a rich bed of blood vessels and immune cells — exactly the cells HIV targets. It tears easily and often invisibly, giving the virus a direct route in. The receptive partner is also exposed to a larger volume of fluid for longer, while the insertive partner's exposure is more limited. That combination puts receptive anal sex at the top, and it explains why the receptive role outranks the insertive role in vaginal sex too.
What raises the risk beyond the baseline
The headline number assumes an average partner with average viral load. Two things push it up sharply:
- Another STI, especially one that causes sores. Having a separate STI raises HIV risk about 2.6 times. Open sores from herpes or syphilis breach the skin barrier, and the inflammation from gonorrhea or chlamydia draws extra HIV-target immune cells to the area — both make it easier for the virus to get in. Test for and treat STIs rather than wait.
- Acute (very recent) HIV in the partner. In the first weeks after someone is infected, before their body mounts a response, their viral load can be extremely high and they're often unaware they have HIV, making transmission more likely than the average figure suggests.
How to lower the risk
The highest-risk activity has the strongest tools. You can stack several so that if one slips, another holds.
- Condoms. A condom puts a physical barrier between fluid and that thin rectal lining and cuts HIV risk sharply. Use plenty of water- or silicone-based lube. Never oil-based, which degrades latex and causes condoms to break, and the tears that lube prevents are exactly what raises risk.
- PrEP. Pre-exposure prophylaxis is daily (or on-demand) medication taken by the HIV-negative partner that cuts HIV risk by about 99% when taken consistently. For receptive anal sex specifically, where baseline risk is highest, PrEP is the single biggest lever you have.
- Layer them. Condoms and PrEP work through different mechanisms and can be used together for more protection than either alone.
- U=U — undetectable equals untransmittable. A partner with HIV who takes treatment and stays virally suppressed does not transmit HIV through sex, full stop. So earlier hiv treatment can help prevention for everyone, not just the person being treated.
When to talk to a clinician
Bring this up with a clinician if you have receptive anal sex with partners whose status you don't know or who aren't on treatment. That's the profile PrEP was designed for, and it's a routine, judgment-free conversation in primary care. If you've had a recent exposure you're worried about, ask about PEP (post-exposure prophylaxis) right away — it has to start within a narrow window after exposure to work. And test on a schedule, because HIV and other STIs are often silent. You can get tested without symptoms, and our guide on when to test after exposure explains how long to wait so a recent exposure doesn't slip through a too-early test.