Circumcising men routinely across Africa could prevent millions of deaths from AIDS, World Health Organization researchers and colleagues reported on Monday.

They analyzed data from trials that showed men who had been circumcised had a significantly lower risk of infection with the AIDS virus, and calculated that if all men were circumcised over the next 10 years, some two million new infections and around 300,000 deaths could be avoided.

Researchers believe circumcision helps cut infection risk because the foreskin is covered in cells the virus seems able to easily infect. The virus may also survive better in a warm, wet environment like that found beneath a foreskin.

So if men were circumcised, fewer would become infected and thus could not infect their female partners.

The human immunodeficiency virus or HIV, which causes AIDS, now infects close to 40 million people and has killed another 25 million. It mostly affects sub-Saharan Africa and the main mode of transmission is sex between a man and a woman.

Several studies have suggested that men who are circumcised have a lower rate of HIV infection. This has been especially noticeable in some parts of Africa, where some groups are routinely circumcised while neighboring groups are not.

Last year, Dr. Bertran Auvert of the French National Research Agency INSERM and colleagues at WHO found that circumcised men in South Africa were 65 percent less likely to become infected with the deadly and incurable virus.

His team then did an analysis to see what would happen if all African men were circumcised.

“In West Africa, male circumcision is common and the prevalence of HIV is low, while in southern Africa the reverse is true,” they wrote in the current report, published in the Public Library of Science Medicine.

“This analysis shows that male circumcision could avert nearly six million new infections and save three million lives in sub-Saharan Africa over the next twenty years,” they wrote.

Overall, they project that universal male circumcision would reduce the rate of infections by about 37 percent.

“Male circumcision alone cannot bring the HIV/AIDS epidemic in Africa under control. Even circumcised men can become infected, though their risk of doing so is much lower,” the journal cautioned in a commentary.