NEW YORK (Reuters Health) - A new study finds that circumcised men appear less likely to sustain cuts, abrasions and other minor injuries to the penis during sex -- which may help explain why circumcision lowers the risk of HIV transmission from heterosexual sex.

For the new study, researchers used data from an HIV clinical trial in Africa, where nearly 2,800 men between the ages of 18 and 24 were randomly assigned to undergo circumcision or remain uncircumcised. In 2005 and 2006, that trial and two others in Uganda, South Africa and Kenya showed that circumcision can reduce a man’s risk of HIV infection through heterosexual sex by up to 60 percent.

In the current study, the researchers found that, over two years, circumcised men were 39 percent less likely than their uncircumcised counterparts to report any type of penile injuries during sex.

This raises the possibility that lower injury risk is one reason that circumcision lowers the odds of HIV transmission, according to the researchers, led by Dr. Supriya D. Mehta of the University of Illinois at Chicago.

Exactly why circumcision may protect against HIV during sex is unknown, Mehta and colleagues report in the Journal of Urology. There are a few theories: One is that, by reducing the amount of mucosal tissue exposed during sex, circumcision limits the virus’ access to the body cells it targets. Another theory is that the thickened skin that forms around the circumcision scar helps block HIV from gaining entry.

But there is also a possible role for mild penile injuries -- cuts, scratches and tears in the skin that could serve as a portal of entry for HIV. In some past studies, uncircumcised men have reported higher rates of such injuries than circumcised men.

At the outset of the current trial, 64 percent of the men said they had sustained some form of penile injury during sex in the past six months -- most often general soreness, scratches, cuts or abrasions. Seventeen percent said they had bleeding.

Six months into the trial, that rate was on the decline. By year two, 31 percent of circumcised men said they’d had a sex-related penile injury in the past six months.

Men in the uncircumcised group also reported a reduction in injuries, though it was less significant -- with 42 percent saying they’d sustained a penile injury in the past six months. That decline, according to Mehta’s team, is likely due to the general improvements both study groups showed in their sexual health practices -- including greater condom use and fewer sex partners.

Men who said they had had multiple sex partners in the past month were more likely to report sex-related penile injuries than those who had been monogamous. On the other hand, condom use and the habit of washing the penis within an hour of having sex were both linked to decreased risks of penile soreness and other injuries.

Further studies, Mehta’s team writes, should look at the role penile injuries may play in the transmission of HIV or other sexually transmitted diseases.

SOURCE: here tract Journal of Urology, online May 17, 2010.