Sexually transmitted infections (STIs) are diseases spread by sexual contact. If you're pregnant, you can also spread them to your baby before or during delivery. STIs are also called sexually transmitted diseases (STDs).

You can be exposed to an STI anytime you have sex or close contact with the genitals, mouth, or rectum of another person. But exposure is more likely if you have more than one sex partner or you don't use condoms. Using condoms can reduce the risk of STIs. STIs can be prevented by not having sexual contact. (This is called abstinence.)

There are at least 20 different STIs. They include chlamydia, gonorrhea, syphilis, and human immunodeficiency virus (HIV), which causes AIDS. STIs caused by bacteria can be treated and cured. STIs caused by viruses, such as HIV, can be treated but not cured.