"Sexually transmitted infections (STIs) are infections you can get by having sex with someone who has an infection. These infections are usually passed by having intercourse, but they can also be passed through anal sex, oral sex or skin-to-skin contact. STIs can be caused by viruses or bacteria. STIs caused by viruses include hepatitis B, herpes, HIV and the human papilloma virus (HPV). STIs caused by bacteria include chlamydia, gonorrhea and syphilis." Read more.