Circumcised men are less likely to contract HIV during unprotected penetrative sex than men who are uncircumcised, according to a new study by the United States Agency for International Development. The report shows a strong association between circumcision and HIV protection, USAID assistant administrator for global health Anne Peterson told The Washington Times. The skin on the underside of the foreskin on uncircumcised men contains many Langerhans' cells, which HIV targets for infection. Bodily fluids can easily be trapped under the foreskin, placing the fluids in direct contact with the cells most vulnerable to infection. Researchers said the cells on the rest of the penis are much more difficult to infect; Edward Green, a Harvard University researcher, has even called them "armor-like." Circumcision also reduces the risk of contracting other sexually transmitted diseases and makes condom use easier, Green said. Green and Peterson both are quick to add, however, that circumcision does not convey absolute protection against HIV and that circumcised men who engage in unprotected sex are still putting themselves at risk for infection.