According to a study published in the online journal of the American Society for Microbiology, circumcision reduces the risk of HIV infection in men by 50-60 percent. It also reduces the risk of infection with human papillomavirus and herpes simplex virus type 2.
Circumcision alters the ecosystem around the penis. It reduces the amount of moisture and increases the amount of oxygen. This makes the area less hospitable for anaerobic bacteria. Circumcised men have a significantly lower load of genital bacteria than uncircumcised men.
Genital bacteria seem to affect how susceptible the penis is to STDs. Instead of helping prevent infection, high amounts of genital bacteria can help the HIV virus infect the body. In uncircumcised men, a high bacterial load can trigger cells that cells that deliver HIV right to the T-cells they wish to infect. Reducing the amount of genital bacteria might prevent this from happening.
The study authors are continuing with their research to discover how the bodies biological mechanisms work and which anaerobes in particular increase the risk of HIV infection.l