A new way of preventing the spread of HIV/AIDS and other sexually transmitted diseases is supported by research published in Nature today (5 January). It involves microbicides, which are gels and creams that a woman applies to her vagina before sex. They kill bacteria and viruses and stop them being transmitted between partners. Over 60 microbicides are being tested, but none has yet made it to the market. They act in different ways, for example by forming a gelatinous physical barrier, like a condom, or by changing the vagina's acidity, as reported by SciDev.