A condom is a sheath-shaped barrier device that may be used during s**ual intercourse to reduce the probability of pregnancy and spreading s**ually transmitted infections (STIs/STDs) such as HIV/AIDS. It is rolled onto an erect pe**is before intercourse and blocks ejaculated semen from entering the body of a s**ual partner. Condoms are also used during fellatio and for collection of semen for use in infertility treatment. 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, often made of nitrile. As a method of birth control, male condoms have the advantages of being inexpensive, easy to use, having few side effects, and offering protection against s**ually transmitted diseases. 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 an 18% 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 s** education classes.