Spermicides are chemical substances that kill sperm, and microbicides are chemical substances that kill viruses. Scientists are currently testing many spermicides and microbicides to see if they can help prevent transmission of STIs, (particularly HIV).
The failure of N-9 (nonoxyl-9) clinical trials as an effective microbicide against HIV and other STIs have not curbed hopes that some agents may yet be helpful, when combined with other methods of protection (e.g. condoms) in reducing risk of HIV infection. Spermicides and condoms with nonoxyl-9 are still on the market. These products should not be used, because they may cause vaginal or anal irritation, and thus may serve as entry points for the virus.