Quick Answer
Per-act HIV transmission risk varies by act: receptive anal ~1.4%, insertive anal ~0.1%, receptive vaginal ~0.08%, insertive vaginal ~0.04%, receptive oral essentially zero. These numbers assume a known HIV-positive partner not on treatment. PEP within 72 hours reduces risk further.
- Receptive anal: highest risk at ~1.4% per act
- Insertive anal: ~0.1% per act
- Receptive vaginal: ~0.08% (8 per 10,000 acts)
- Receptive oral: essentially zero
Context Most Pages Skip
Per-act risk is low, but cumulative risk over multiple acts with an untreated positive partner is substantial. These numbers are why PrEP exists.
Putting It in Perspective
A 1.4% risk per act of receptive anal sex means 1 infection per ~71 acts. Over a year of weekly unprotected sex, the cumulative risk approaches 50%. PrEP reduces this to essentially zero.
⚕️ This page is educational and does not replace advice from a licensed clinician. If you may have been exposed to an STI, get tested — most infections are manageable, and many are fully curable.
Sources & Further Reading
- CDC — Sexually Transmitted Infections
- CDC STI Treatment Guidelines
- WHO — Sexually transmitted infections fact sheet
- MedlinePlus — Sexually Transmitted Diseases
Figures reflect CDC surveillance and WHO estimates; they are population statistics, not personal risk predictions.