HIV Risk From a Single Exposure
"Can you get HIV from one time?" is one of the most searched HIV questions. The honest answer is yes, it is possible, but for almost every single exposure the chance is low, and most single exposures do not lead to HIV, even when the partner has HIV.
The numbers for one act
For a single act with a partner who has HIV and is not on treatment, published per-act estimates are:
- Receptive anal sex: roughly 1.4% (about 1 in 70)
- Insertive anal sex: roughly 0.11% (about 1 in 900)
- Receptive vaginal sex: roughly 0.08% (about 1 in 1,250)
- Insertive vaginal sex: roughly 0.04% (about 1 in 2,500)
- Oral sex: very low; see HIV risk from oral sex
- Sharing injection equipment: roughly 0.63% (about 1 in 160)
These are averages. Bleeding, another sexually transmitted infection, or a partner who was very recently infected can raise the risk. A condom, PrEP, or a partner on effective treatment lowers it a lot.
When you don't know your partner's status
Most people who worry about "one time" do not know their partner's status. In that case the real risk is the per-act figure multiplied by the chance that the partner has HIV at all. For example, if about 1 in 250 adults has HIV where the encounter happened, a single receptive vaginal exposure with a partner like an average adult works out to roughly 1 in 300,000. Among some groups, such as gay and bisexual men in many countries, more partners have HIV, so the risk is higher.
That is exactly what our HIV risk calculator does: it combines the type of exposure, the country and other factors into one estimate.
Why one time can still matter
A low probability is not zero. That is why it makes sense to act on a real exposure instead of only reading about it:
- Within 72 hours: if your partner has HIV or you do not know, and the act was anal or vaginal sex without a condom, ask a doctor, emergency department or sexual health clinic about PEP today.
- Afterwards: test at the right time. A 4th-generation lab test at 45 days is highly reassuring, and antibody tests are conclusive at 90 days. See the testing guide.
Symptoms are not a guide
Many people feel unwell after a frightening encounter, often from anxiety alone. Early HIV infection can cause flu-like symptoms, but many people with HIV have none. Symptoms can neither confirm nor rule out HIV; only a test can. See HIV symptoms and the infection timeline.