How does circumcision reduce the risk of HIV infection?

There is now a compelling body of epidemiological evidence which shows that male circumcision provides significant protection against HIV infection.

As detailed above, the first ever randomized controlled trial (RCT) of male circumcision as an HIV prevention measure, presented at the 3^rd IAS Conference in 2005 produced strong evidence of a protective effect. There were only 35% as many infections in the circumcision arm as opposed to the control arm, implying that circumcision can prevent at least six out of ten female-to-male HIV transmissions, and possibly up to three-quarters of transmissions.

Previous cohort studies have shown that circumcised males are two to eight times less likely to become infected with HIV. Furthermore, circumcision also protects against other sexually transmitted infections, such as syphilis and gonorrhoea, and since people who have a sexually transmitted infection are two to five times more likely to become infected with HIV, circumcision may be even more protective.

It is worth remembering that the majority of men who are HIV-positive have been infected through the penis. Cells, called Langerhans cells, which line the inner surface of the foreskin. These cells have HIV receptors and are likely to be the primary point of viral entry into the penis of an uncircumcised man.

A 2002 report by the US Agency for International Development (USAID) was based on a systematic review of 28 scientific studies published by the London School of Hygiene and Tropical Medicine. The Washington Times reported that "a sub analysis of 10 African studies found a 71% reduction among higher risk men". Edward G. Green, a senior researcher at Harvard University told the Washington Times that if all males in Africa were circumcised, the HIV/AIDS prevalence rate could be reduced from 20 percent in some regions to below 5 percent.

In one study of couples in Uganda where the woman was HIV-positive and her male partner was not, no new infections occurred among any of the 50 circumcised men over 30 months, whereas 40 of 137 uncircumcised men became infected during this time. Both groups had been given free access to HIV testing, intensive instruction about preventing infection, and free condoms (which were continuously available), but 89% of the men never used condoms, and condom use did not seem to influence the rate of transmission of HIV.