Condoms are the only contraceptive method proven to reduce the risk of all sexually transmitted infections (STIs), including HIV. They can be used as a dual-purpose method, both for prevention of pregnancy and protection against STIs.
Estimated pregnancy rates during perfect use of condoms, that is for those who report using the method exactly as it should be used (correctly) and at every act of intercourse (consistently), is 3 percent at 12 months.
The most frequently cited condom effectiveness rate is for typical use, which includes perfect and imperfect use (i.e. not used at every act of intercourse, or used incorrectly). The pregnancy rate during typical use can be much higher (10-14%) than for perfect use, but this is due primarily to inconsistent and incorrect use, not to condom failure. Condom failure – the device breaking or slipping off completely during intercourse – is uncommon.
Laboratory studies have found that viruses (including HIV) do not pass through intact latex condoms even when devices are stretched or stressed.
In Thailand, the promotion by the government of 100% condom use by commercial sex workers led to a dramatic increase in the use of condoms (from 14% in 1990 to 94% in 1994); an equally dramatic decline in the nation-wide numbers of bacterial STD cases (from 410,406 cases in 1997 to 27,362 cases in 1994); and reduced HIV prevalence in Thai soldiers.
The most convincing data on the effectiveness of condoms in preventing HIV infection has been generated by prospective studies undertaken on serodiscordant couples, when one partner is infected with HIV and the other is not. These studies show that, with consistent condom use, the HIV infection rate among uninfected partners was less than 1 percent per year. Also, in situations where one partner is definitely infected, inconsistent condom use can be as risky as not using condoms at all.
Latex allergies are very rare among the general population. While 1-2 billion condoms are used per year in the USA, the FDA only received 44 reports of allergic reactions associated with condom use between October 1988 and end of 1991. The Centres for Disease Control, Atlanta, USA estimate that the population risk of an allergic reaction to latex is 0.08% and the nature of the reaction tends to be very mild. Concerns about latex allergies should not inhibit sexually active people who are at risk of exposure to pregnancy and STIs using condoms, since the risks associated with unprotected sexual contact are far greater than those from exposure to latex.