A condom is a sheath-shaped barrier device used during sexual intercourse to reduce the probability of pregnancy or a sexually transmitted infection (STI). There are both male and female condoms. With proper use—and use at every act of intercourse—women whose partners use male condoms experience a 2% per-year pregnancy rate. With typical use the rate of pregnancy is 18% per-year. Their use greatly decreases the risk of gonorrhea, chlamydia, trichomoniasis, hepatitis B, and HIV/AIDS. They also to a lesser extent protect against genital herpes, human papillomavirus (HPV), and syphilis. The male condom is rolled onto an erect penis before intercourse and works by forming a physical barrier which blocks semen from entering the body of a sexual partner. Male condoms are typically made from latex and, less commonly, from polyurethane, polyisoprene, or lamb intestine. Male condoms have the advantages of ease of use, easy to access, and few side effects. In those with a latex allergy a polyurethane or other synthetic version should be used. Female condoms are typically made from polyurethane and may be used multiple times.