How to use this page: if you haven’t already, use the 72-hour countdown and the 3-question self-check above for a quick answer. The guide below explains what sits behind that answer, so you can understand your own situation and talk it through with a doctor.
Key takeaways
- PEP is usually recommended after anal or vaginal sex without a condom (or when a condom broke), shared needles or a needle-stick injury, when the other person’s HIV status is unknown or they are not on effective treatment.
- Receptive anal sex carries the highest sexual risk. Oral sex, kissing, biting and spitting carry very low or negligible risk, and PEP is rarely needed.
- If your partner has HIV and a sustained undetectable viral load, HIV is not passed on through sex (U=U).
- PEP must start within 72 hours. If you are unsure, contact a clinic now rather than waiting to decide.
- Past 72 hours, PEP is no longer an option, but testing, advice and PrEP still are.
Do I need PEP? The short answer
You may need PEP if three things are true: blood, semen, pre-seminal fluid, vaginal fluids or rectal fluids from another person could have entered your body; that person has HIV or you don’t know their status; and the exposure happened less than 72 hours ago.
If all three apply, a doctor should assess you today. If you are not sure whether they apply, that uncertainty is itself a good reason to ask. If you want to understand the medicine itself first, read what PEP is and how it works.
HIV risk by type of exposure
Not all exposures carry the same risk. The figures below come from the CDC’s HIV risk and prevention estimates, which give the estimated chance of HIV being passed on per 10,000 exposures to a source with HIV, when no condom, PEP, PrEP or treatment is involved.
| Type of exposure | Estimated risk per 10,000 exposures (CDC) | Relative risk | Is PEP usually recommended? |
|---|---|---|---|
| Receptive anal sex (“bottom”) | 138 | High | Yes, if the partner’s status is unknown or they are not on effective treatment |
| Sharing needles to inject drugs | 63 | High | Yes |
| Needle-stick injury | 23 | Moderate | Usually, if the source is known or likely to have HIV; assessed case by case |
| Insertive anal sex (“top”) | 11 | Moderate | Usually, if the partner’s status is unknown or they are not on effective treatment |
| Receptive vaginal sex | 8 | Moderate | Usually, if the partner’s status is unknown or they are not on effective treatment |
| Insertive vaginal sex | 4 | Lower | Often, depending on the partner and other factors |
| Giving or receiving oral sex | Low | Very low | Rarely; discussed case by case |
| Biting, spitting, sharing sex toys | Negligible | Very low | Not usually |
| Kissing, hugging, sharing cups or toilets | Not a route of HIV transmission | None | No |
These are averages across many people, not a prediction for you. A single exposure can lead to infection even when the average risk is low, which is why doctors look at the full picture rather than a number alone.
What changes your risk?
A doctor will ask about the details below, because each one can push the risk up or down.
Your partner’s HIV status and viral load (U=U)
If your partner has HIV, takes treatment and has a sustained undetectable viral load, they do not pass HIV on through sex. This is known as undetectable = untransmittable, or U=U. In that case PEP is usually not needed after sex. If they have HIV but are not on treatment, or their viral load is unknown or high, the risk is higher and PEP is usually advised.
Condoms
A condom that stayed intact and on throughout sex is very effective protection. If it broke, slipped off, or was only used for part of the time, treat the exposure as unprotected.
Other sexually transmitted infections
Having an STI such as syphilis, gonorrhoea or herpes, in either partner, can make HIV easier to pass on, especially if there are sores or inflammation.
Bleeding, injury and ejaculation
Bleeding, tears or rough sex increase the risk, as does ejaculation inside the body. Sexual assault often involves several of these factors, and PEP is usually offered.
When the source is unknown
If you don’t know your partner’s status, doctors consider how common HIV is in that partner’s likely community, the type of exposure and the other factors above. An unknown status does not automatically mean PEP, but with anal or vaginal sex it often does.
When is PEP usually recommended?
Doctors most often recommend PEP after:
- Anal or vaginal sex without a condom, or when a condom broke or slipped, with a partner of unknown status or a partner with HIV who is not virally suppressed
- Sexual assault
- Sharing needles, syringes or other injecting equipment
- A needle-stick injury or blood splash into the eyes, mouth or broken skin, where the source may have HIV
If you have been sexually assaulted, your safety comes first. In Thailand you can call 1669 for emergency medical help or the Tourist Police on 1155. PEP can be started alongside emergency care, and a clinic can also discuss emergency contraception and STI checks. For a step-by-step plan for this and other situations, see what to do after a possible HIV exposure.
When you probably don’t need PEP
PEP is not usually needed after:
- Kissing, including deep kissing, hugging, massage or touching
- Sharing food, drinks, towels, toilets or swimming pools
- Sex with a condom that stayed intact
- Sex with a partner on HIV treatment with a sustained undetectable viral load
- Contact with saliva, sweat, tears or urine, when no blood is present
- Oral sex in most situations, although a doctor may look at the details, such as bleeding gums or mouth sores
If you still feel anxious, that is understandable: a test and a short conversation with a doctor can reassure you.
What if my partner says they are HIV-negative?
A recent negative test is useful information, but it may not reflect very recent infections, because tests have a window period. Doctors take a partner’s negative result into account, together with how recent it was and whether there could have been risks since. Don’t let waiting for their new result use up your 72 hours.
What if it’s been more than 72 hours?
After 72 hours, PEP is no longer recommended, because HIV may already have established an infection and the medicines are unlikely to help. This does not mean there is nothing you can do:
- Get tested at the right times. A baseline test now, and further tests once the window period has passed. Our guide on when to test for HIV after an exposure sets out the timings.
- Check for other STIs. Several can be treated quickly once found.
- Look after yourself and your partners. Use condoms until your results are clear.
- Plan ahead. If exposures are likely again, PrEP may suit you better than repeated PEP.
Frequently asked questions about whether you need PEP
Do I need PEP after oral sex?
Usually not, because the risk is very low. A doctor may look more closely if there was ejaculation in the mouth along with bleeding gums or mouth sores, or if the partner is known to have HIV and is not on treatment.
Do I need PEP if the condom broke but my partner didn’t ejaculate?
The risk is lower, but not zero, because pre-seminal and other fluids can carry HIV. With a partner of unknown status, it is worth speaking to a doctor while you are still in the 72-hour window.
Do I need PEP if I am already on PrEP?
If you have been taking PrEP as prescribed, you are usually protected and PEP is not needed. If you have missed doses or recently started, ask a doctor.
Can I use this page instead of seeing a doctor?
No. The self-check and this guide help you understand your risk, but only a doctor can assess your situation properly. If in doubt, message us for a confidential assessment.
If you think you might need PEP, the most useful thing you can do now is talk to a doctor. Our clinic near BTS Asok welcomes walk-ins every day from 09:00 to 21:00, and you can see what a visit includes on our PEP, PrEP and HIV testing services page.