Does Anal Sex Cause HIV? HIV and STD Risk From One Time With a Man
Does anal sex cause HIV? No. Anal sex cannot create HIV. It passes the virus on only when one partner already has it.
But if a partner has HIV and is not on treatment, anal sex carries the highest risk of any kind of sex. The bottom carries most of that risk (CDC, HIV.gov).
One time without a condom can be enough. Still, the odds for a single act are lower than most men fear. Below are the numbers for bottoms, tops and oral sex, what changes them, the other STDs to think about, and what to do in the next 72 hours.
HIV Odds From One Time: Bottom, Top and Oral
If your partner has HIV and is not on treatment, the CDC puts the chance of getting HIV from one act of receptive anal sex (being the bottom) at 138 in 10,000, about 1 in 72. For the top, it is 11 in 10,000, about 1 in 909. HIV from oral sex is extremely rare.
| Type of sex, one time, no condom | Chance per act if he has HIV and is not on treatment | About |
|---|---|---|
| Receptive anal sex (bottom) | 138 in 10,000 | 1 in 72 |
| Insertive anal sex (top) | 11 in 10,000 | 1 in 909 |
| Receptive vaginal sex, for comparison | 8 in 10,000 | 1 in 1,250 |
| Oral sex | Extremely rare (CDC) | — |
| He has HIV, takes treatment, and his viral load stays undetectable | No HIV through sex | 0 |
Source: CDC HIV Risk Estimator, based on Patel et al., AIDS, 2014.
If you don't know his HIV status
These numbers assume your partner has HIV. Most one-time partners do not, so your real odds are usually lower.
How much lower depends on who he was. An older U.S. study of 2,189 gay and bisexual men, done in 1992–1994, counted partners who had HIV or whose status was unknown. The risk per act was about 0.27% for the bottom (about 1 in 370), 0.06% for the top, and 0.04% for giving oral sex with ejaculation in the mouth (Vittinghoff et al., 1999).
Those figures come from before PrEP and modern HIV treatment, so treat them as a rough guide only.
Not knowing is common. In 2022, about 13 of every 100 people with HIV in the U.S. did not know they had it (CDC).
In my experience, most men who come in asking "Does anal sex cause HIV?" after one time test negative. But the odds can't tell you which group you are in. Only a test can.
For sex with a woman, see the odds of getting an STD from one heterosexual encounter.
Why Does Anal Sex Cause HIV More Easily Than Other Sex?
The reason is the rectum. HIV can enter the body through the lining of the rectum (CDC). That lining is very thin, which is why being the bottom is the riskiest kind of sex for HIV. HIV can be in semen and in pre-cum (IAPAC, 2025).
The rectum is also full of immune cells, the cells HIV infects (CATIE). That helps explain why receptive anal sex carries about 17 times the risk of receptive vaginal sex: 138 versus 8 in 10,000 (CDC).
HIV also travels the other way. Rectal fluid, the mucus that lines the rectum, can carry HIV.
In one study of 64 men with HIV, the average amount of virus in their rectal fluid was higher than in their semen and blood (CATIE). That is one way a top can get HIV from a bottom.
Does anal sex cause AIDS?
No. AIDS is the third and most serious stage of HIV infection, not a separate disease caused by a type of sex (HIV.gov). Anal sex can pass on HIV. Without treatment, HIV can later progress to AIDS.
Chances of Getting HIV as a Bottom
Can you get HIV from anal sex as the bottom? Yes. Your chance from one act with a partner who has untreated HIV is about 1 in 72 (CDC).
Being the bottom makes you more likely to get HIV than being the top (CDC). By the CDC's numbers, the bottom's risk is more than 12 times the top's: 138 versus 11 in 10,000.
Can you get HIV without ejaculation?
Yes. Pulling out before he ejaculates may lower the bottom's risk, but it does not remove it. Pre-cum can carry HIV too (IAPAC, 2025).
Circumcision does not protect the bottom (IAPAC, 2025).
Can a Top Get HIV From a Bottom?
Yes. Either partner can get HIV during anal sex (CDC). Your chances of getting HIV as a top, from one act with a partner who has untreated HIV, are about 1 in 909 (CDC). That is much lower than the bottom's risk, but it is not zero.
HIV gets in through the opening at the tip of the penis, the foreskin, or small cuts and sores on the penis (CDC). It comes from the bottom's rectal fluid or blood (CATIE).
So can tops get HIV from topping once? Yes, it is possible, even if the odds are low. Two points matter for tops:
- Pulling out does not protect the top (IAPAC, 2025).
- A circumcised top may have a lower risk (IAPAC, 2025).
What Raises or Lowers the Odds of HIV
The odds per act change a lot with treatment, protection and other infections. The CDC's HIV Risk Estimator gives these effects, and the PARTNER2 study measured the first one in gay couples.
| What changes | Effect on HIV risk |
|---|---|
| He takes HIV treatment and his viral load stays undetectable | No HIV through sex. In PARTNER2, 782 gay couples reported more than 76,000 acts of condomless sex with no HIV passed within the couple (The Lancet, 2019) |
| You take PrEP as prescribed | About 99% lower (CDC) |
| A condom, if you are the bottom | 72% lower (CDC) |
| A condom, if you are the top | 63% lower (CDC) |
| He got HIV in the last few weeks | About 7 times higher (CDC) |
| You have another STD | About 2.7 times higher (CDC) |
Viral load, the amount of HIV in the blood, is highest in the first 2 to 4 weeks after someone gets HIV (CDC). That is why a recent infection is the riskiest.
PrEP is medicine you take before sex to prevent HIV. Condoms also protect against some other STDs, such as gonorrhea and chlamydia (HIV.gov).
Other STDs From One Time With a Man
Chlamydia, gonorrhea, syphilis and herpes all spread through anal and oral sex. Unlike HIV, they have no reliable one-time odds for sex between men. What is known matters more: in the rectum and throat, these infections often cause no symptoms (CDC).
| STD | Where it can show up after sex with a man | Symptoms | |
|---|---|---|---|
| Chlamydia | Rectum; urethra (the tube inside the penis) | Often none in the rectum (CDC) | chances of getting chlamydia |
| Gonorrhea | Rectum, throat, urethra | Often none in the rectum or throat (CDC) | gonorrhea transmission odds |
| Syphilis | A sore where it entered: anus, mouth or penis | The sore is usually painless and easy to miss (CDC) | syphilis pictures |
| Herpes | Sores on the anus, penis or mouth | Most people have no symptoms or very mild ones (CDC) | chances of getting herpes |
Gay and bisexual men made up 43% of all early-stage (primary and secondary) syphilis cases in the U.S. in 2020 (CDC, reported in 2022).
Because these infections are often silent, testing is the only way to find them. See how to test below.
What to Do in the First 72 Hours
If you had anal sex without a condom with a man who has HIV, or whose status you don't know, ask a doctor about PEP today. PEP (post-exposure prophylaxis) is 28 days of HIV medicine. It must start within 72 hours, and the sooner the better (CDC).
- Ask about PEP right away. Start it as soon as possible, ideally within 24 hours, and no later than 72 hours after sex (CDC). PEP is for emergencies. See HIV PEP.
- Ask about doxy-PEP if you had an STD this past year. The CDC recommends that doctors offer doxy-PEP, one 200 mg dose of the antibiotic doxycycline taken within 72 hours after sex, to gay and bisexual men and transgender women who had syphilis, chlamydia or gonorrhea in the past 12 months. In studies, it cut syphilis and chlamydia by more than 70% and gonorrhea by about 50% (CDC, 2024).
- If this happens often, ask about PrEP. The CDC advises PrEP, not repeated PEP, for people who may be exposed again and again.
At STD Center NY, we prescribe both PEP and doxy-PEP.
An HIV test today cannot show an infection from this encounter yet. It shows whether you had HIV before it.
When and How to Test After Sex With a Man
Test for HIV after the window period, the time a test needs to pick up a new infection. And test every place you had sex: penis, rectum and throat.
| HIV test | Can usually find HIV this long after sex |
|---|---|
| Nucleic acid test (NAT), blood from a vein | 10 to 33 days |
| Lab antigen/antibody test, blood from a vein | 18 to 45 days |
| Rapid antigen/antibody test, finger stick | 18 to 90 days |
| Antibody test | 23 to 90 days |
Source: CDC, 2026. These times assume no HIV medicine; PEP or PrEP can delay when a test turns positive (CDC). If you take PEP, test again 4 to 6 weeks and 12 weeks after the exposure (CDC).
For chlamydia and gonorrhea, the CDC tells doctors to test men who have sex with men at each site used:
- Urine, if you were the top.
- Rectal swab, if you were the bottom.
- Throat swab for gonorrhea, if you gave oral sex. The CDC does not recommend throat testing for chlamydia.
Testing urine alone can miss about 70% of chlamydia and gonorrhea infections in men who have sex with men (CDC). For how soon each test works, see when to test for each STD after sex.
For sexually active gay and bisexual men, the CDC advises STD testing at least once a year, and every 3 to 6 months if the risk continues.
Testing at STD Center NY
At STD Center NY, the doctor sees every patient. We test for HIV, syphilis, chlamydia and gonorrhea at each site you had sex.
Rapid tests, results in 30 minutes. The price is the total. There is no office visit fee on top.
- Rapid HIV test (fourth generation, antigen/antibody): $90.
- Rapid HIV and syphilis test: $130.
- Rapid syphilis test: $80.
Lab tests. Throat and rectal swabs for chlamydia and gonorrhea go to the lab, Northwell or Quest. Results take 3 to 5 days.
- If we take your insurance, it covers the visit and the lab tests. Your plan sets any copay or deductible.
- If we don't take your plan, the office visit is $90. The lab still bills your insurance.
- With no insurance, the office visit is $90 and the lab bills you directly.
If a rapid HIV test is positive, we draw blood to confirm it at the lab. Results take 5 to 7 days. We diagnose HIV and refer you for treatment.
See our rapid HIV test page for details.
