A condom is a sheath-shaped barrier device that may be used during sexual intercourse to reduce the probability of pregnancy and decrease the risk of sexually transmitted infections (STIs) such as HIV/AIDS. It is rolled onto an erect penis before intercourse and blocks ejaculated semen from entering the body of a sexual 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 rubber.