A rather and confusing and counter-intuitive report came out earlier this week, when scientists announced that uncircumcised men who wash their penis after sex are increasing their risk of AIDS.

This is of course contrary to all common sense. Washing after sex, and hygeine generally, is always presented as the way to avoid sexually transmitted infections. So it's not clear why the longer the men waited to wash after sex, the lower their risk of HIV infections became.

Unfortunately, the scientists didn't ask the men how exactly they washed, according to the New York Times, which reported the story on Tuesday. This could be important because the soaps used in Africa are more irritating than the ones in the US, for example, and could be contributing to the bizarre observation. The researchers say it's also possible that vaginal secretions, which are acidic, may be harming the virus. The latter seems unlikely to me — surely if vaginal secretions offered some protection, women would not now be the brunt of the epidemic?

In any case, resolving this seemingly contradictory study is important so public health workers can spread the right message about cleanliness — and not unwittingly put men even more at risk.