Sexually transmitted infections (STIs) are diseases transmitted through genital contact with another person. They can affect people of all ages, orientations, and backgrounds. Common STIs include hepatitis, syphilis, gonorrhea, chlamydia, herpes, HPV, and HIV. STIs are transmitted through unprotected vaginal, anal, and oral sex. Using condoms during sex can help prevent transmission of STIs. Many STIs have no symptoms, so it is important to get regular checkups and testing. While treatable with medication if caught early, left untreated STIs can cause serious health problems.