Gels or creams that can be inserted into the rectum or vagina, designed to reduce the risk of anal or vaginal transmission of viruses such as HIV (see also AIDS/HIV). The aim is to kill or to inactivate the virus, creating a barrier to mucosal cells or preventing the infection from taking hold after it has entered the body. The results of a number of large-scale trials have had variable results, largely because it is clear that social, psychological and educational factors play a big part in determining whether at-risk persons will use them.