Latex condoms can provide up to 98-99 percent protection against pregnancy and most STDs, including HIV infection, but only if they are used consistently and correctly.
The proper and consistent use of latex condoms when engaging in sexual intercourse-vaginal, anal, or oral--can greatly reduce a person's risk of acquiring or transmitting sexually transmitted diseases (STDs), including HIV infection.
Sexually transmitted infections are preventable. The use of barriers which prevent contact with infectious sores or fluids is one strategy for reducing risk. The latex condom provides a continuous mechanical barrier which affords excellent protection against a wide variety of bacteria, viruses, and other germs. Aside from preventing HIV infection directly, widespread condom use could have a substantial indirect impact on the HIV epidemic by preventing other STDs, some of which increase the risk of HIV transmission.
Under laboratory conditions, viruses occasionally have been shown to pass through natural membrane ("skin" or lambskin) condoms, which contain natural pores and are therefore not recommended for disease prevention. On the other hand, laboratory studies have consistently demonstrated that latex condoms provide a highly effective mechanical barrier to HIV. Although the ability of latex to serve as an effective mechanical barrier to HIV and sperm in the laboratory is encouraging, clinical studies typically show failure rates ranging from 2 to 15 percent when condoms are the only method used to prevent pregnancy. Why is there such a large range in the observed effectiveness in reports of actual use compared with the consistent laboratory findings? The answer to this question has important implications for HIV prevention and lies in an understanding of the key role that proper use plays in condom efficacy. A condom is a highly effective mechanical barrier when it is used consistently and correctly. However, studies have shown that only 30 to 60 percent of men who claim to use condoms for contraception actually used them for every act of intercourse. Further, even people who use condoms consistently may not use them correctly. Incorrect use contributes to the possibility that the condom could leak from the base or break. 
Numerous studies among sexually active people have demonstrated that a properly used latex condom provides a high degree of protection against a variety of STDs, including HIV infection. The degree of protection that proper use of latex condoms provides against HIV transmission is most evident from studies of couples in which one member is infected with HIV and the other is not (i.e., "discordant couples"). Such studies suggest a 70 to 100 percent reduction in the risk of acquiring HIV infection in couples reporting consistent condom use. The extreme importance of using condoms consistently and correctly is emphasized by a study of 563 discordant couples in Europe. Among the 44 couples who used condoms inconsistently, 6 of the uninfected partners became infected. In contrast, among the 24 couples who reported consistent condom use, none of the uninfected partners became infected.
Condoms are classified as medical devices and are regulated by the Food and Drug Administration. Each latex condom manufactured in the United States is tested for defects, including holes, before it is packaged, and several studies clearly show that condom breakage rates in this country are less than 2 percent. One study showed that even when condoms do break, more than half of such breaks occurred prior to ejaculation.
(Centers for Disease Control and Prevention, HIV/AIDS Prevention Training Bulletin, February, 1993.)
