Barrier contraceptives are birth control methods that physically or chemically keep sperm from reaching an egg. According to the American College of Obstetricians and Gynecologists (ACOG), they include external and internal condoms, spermicide, the contraceptive sponge, diaphragms, and cervical caps.
Some barrier methods—especially latex and polyurethane external condoms—also help reduce the risk of sexually transmitted infections, including HIV, while others (such as diaphragms and cervical caps used with spermicide) primarily prevent pregnancy and do not protect against STIs. ACOG notes barrier methods are generally less effective at preventing pregnancy than implants, injections, or IUDs, and work best when used correctly every time.