Sexually transmitted infections (STIs) can have varied symptoms depending on the infection, and some symptoms may be similar to other non-STI illnesses. Common STI symptoms include abnormal discharge, bleeding between periods, and sores or pain in the genital area. The only way to know for sure if you have an STI is to get tested, even without symptoms. It's important to get tested yearly if sexually active, after unprotected sex, if a partner has an STI, or if any STI symptoms appear. Using condoms correctly during any sexual activity can help prevent STIs, but abstinence is the only way to be certain of avoiding infection.