Three large clinical trials -- involving thousands of men in Africa -- have shown that male circumcision reduces risk of HIV acquisition. The protection afforded by circumcision is high, with efficacy estimates ranging between 50% and 60%. Some researchers estimate that circumcision helps prevent HIV infection for the male partner simply because it decreases the surface area of skin potentially exposed to HIV infection during sex. Other researchers have a different theory, and it involves the bacteria found on our skin.

At the Conference at Retroviruses and Opportunistic Infections (CROI) held last month, Lance Price, from George Washington University presented compelling research supporting a theory linking the penile microbiome (the colonies of bacteria found on the penis) to HIV risk.

"It's likely that the bacteria living on our genitalia can affect our HIV risk. Bacteria, interacting with our immune system, can make us more or less susceptible to HIV," he explained.

This excerpt was cross-posted with the permission of BETAblog.org. Read the full article.