A condom (US /ˈkɒndəm/ or UK /ˈkɒndɒm/) is a barrier device most commonly used during sexual intercourse to reduce the probability of pregnancy and spreading sexually transmitted diseases (STDs—such as gonorrhea, syphilis, and HIV). It is put on a man's erect penis and physically blocks ejaculated semen from entering the body of a sexual partner. Because condoms are waterproof, elastic, and durable, they are also used in a variety of secondary applications. These include collection of semen for use in infertility treatment as well as non-sexual uses such as creating waterproof microphones and protecting rifle barrels from clogging.
In the modern age, condoms are most often made from latex, but some are made from other materials such as polyurethane, polyisoprene, or lamb intestine. A female condom is also available, most often made of nitrile. As a method of birth control, male condoms have the advantage of being inexpensive, easy to use, having few side effects, and of offering protection against sexually transmitted diseases.
However, according to a study in the Sexually Transmitted Diseases Journal of the American Sexually Transmitted Diseases Association condoms have a breakage rate of 2.3% and a slippage rate of 1.3% which "may translate into a high risk for individuals who are very sexually active." With proper knowledge and application technique—and use at every act of intercourse—women whose partners use male condoms experience a 2% per-year pregnancy rate with perfect use and a 15% per-year pregnancy rate with typical use.
Condoms have been used for at least 400 years. Since the 19th century, they have been one of the most popular methods of contraception in the world. While widely accepted in modern times, condoms have generated some controversy, primarily over what role they should play in sex education classes. They are considered unacceptable in almost all situations by certain religions, notably the Catholic church.
Condoms interfere with the process of paternal tolerance, by which exposure of a woman's immune system to semen during unprotected sex may decrease the risk of pregnancy complications in subsequent pregnancies.