When it comes to sex, nothing is risk-free. Any sexual contact with the penis, vagina, anus, or mouth can spread a sexually transmitted infection (STI). These include chlamydia, gonorrhea, herpes, HIV, and genital warts. The only sure way to prevent STIs is not having sex (abstinence). But there are ways to make sex safer. Use a latex condom each time you have sex. And choose your partner wisely.