HIV Risk Behaviors

The risk of getting HIV varies widely depending on the type of exposure or behavior (such as sharing needles or having sex without a condom). Some exposures to HIV carry a much higher risk of transmission than other exposures. For some exposures, while transmission is biologically possible, the risk is so low that it is not possible to put a precise number on it. But risks do add up over time. Even relatively small risks can add up over time and lead to a high lifetime risk of getting HIV.  In other words, there may be a relatively small chance of acquiring HIV when engaging in a risk behavior with an infected partner only once; but, if repeated many times, the overall likelihood of becoming infected after repeated exposures is actually much higher. 

The table below lists the risk of transmission per 10,000 exposures for various types of exposures.

Estimated Per-Act Probability of Acquiring HIV from an Infected Source, by Exposure Act*

Estimated Per-Act Probability of Acquiring HIV from an Infected Source, by Exposure Act
Type of Exposure Risk per 10,000 Exposures
Blood Transfusion 9,250
Needle-Sharing During Injection Drug Use 63
Percutaneous (Needle-Stick) 23
Receptive Anal Intercourse 138
Insertive Anal Intercourse 11
Receptive Penile-Vaginal Intercourse 8
Insertive Penile-Vaginal Intercourse 4
Receptive Oral Intercourse Low
Insertive Oral Intercourse Low
Biting Negligible
Spitting Negligible
Throwing Body Fluids (Including Semen or Saliva) Negligible
Sharing Sex Toys Negligible

* Factors that may increase the risk of HIV transmission include sexually transmitted diseases, acute and late-stage HIV infection, and high viral load. Factors that may decrease the risk include condom use, male circumcision, antiretroviral treatment, and pre-exposure prophylaxis. None of these factors are accounted for in the estimates presented in the table.

^ HIV transmission through these exposure routes is technically possible but unlikely and not well documented.


  • Patel P, Borkowf CB, Brooks JT. Et al. Estimating per-act HIV transmission risk: a systematic review. AIDS. 2014. doi: 10.1097/QAD.0000000000000298.
  • Pretty LA, Anderson GS, Sweet DJ. Human bites and the risk of human immunodeficiency virus transmission. Am J Forensic Med Pathol 1999;20(3):232-239.
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