Anal intercourse

  • Anal sex without condoms is one of the highest-risk means of sexual HIV transmission.
  • For unprotected anal intercourse with an HIV-positive partner, estimated risks of infection per act range from 0.06 to 0.82% depending on sexual position.

Unprotected (i.e. condomless) anal intercourse is a highly efficient way of transmitting HIV, and it is considered a high-risk activity for both partners, although the exact degree of risk can depend on many factors. For each unprotected act with an HIV-positive partner, the risk of infection has been estimated at 0.82% and 0.06% for the receptive and insertive partners respectively,1 but may be ten to 25 times higher if the positive partner is recently infected.

The receptive or 'passive' partner is at risk of infection from HIV in the semen and pre-seminal fluids ('pre-cum') of the infected partner. Rectal tissue is delicate and easily damaged, which can give the virus direct access to the bloodstream. However, such tissue damage is not necessary for infection to occur: the rectal tissue itself is rich in cells which are directly susceptible to infection.

The insertive or 'active' partner is also at risk of infection, as high levels of HIV can be present in secretions and blood from the rectal tissues. This creates a risk of transmission to the insertive partner through the tissue in the urethra and on the head of the penis – particularly underneath the foreskin.

Studies have identified a number of factors that increase the risk of transmission even further, including sexually transmitted infections and poppers use; these are discussed below, under Co-factors affecting risks. However, unprotected anal intercourse remains a high-risk activity even without these additional risk factors.

References

  1. Vittinghoff E et al. Per-contact risk of human immunodeficiency virus transmission between male sexual partners. American Journal of Epidemiology 150: 306-311, 1999
This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.
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This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.