Hypo-allergenic condom. Latex-free male condom (prophylactic) on a hand. This hypo-allergenic condom is made from polyurethane to lessen the risk of an allergic reaction. A condom is a contraceptive rubber sheath that is unrolled over the erect penis prior to sexual intercourse. This prevents the sperm from entering the vagina and causing pregnancy. Condoms also prevent the spread of sexually-transmitted diseases, including HIV (human immunodeficiency virus) the virus that causes AIDS (acquired immune deficiency syndrome). The use of condoms is one example of safe sex", where sexual activity is modified to reduce the risk of contracting venereal diseases."