Condoms for the Prevention of HIV and STI Transmission
Condoms are physical barriers that can reduce the risk of a sexual exposure to HIV and sexually transmitted infections (STIs). They are made of materials that do not allow HIV or STIs to pass through them. Condoms can be highly effective against HIV and STI transmission when used consistently and correctly. They are much less protective if used inconsistently and/or incorrectly.
What Types of Condoms Are Available to Prevent HIV Transmission?
Two types of condoms are available to prevent the sexual transmission of HIV and other STIs:
How Do Condoms Prevent the Sexual Transmission of HIV and STIs?
Condoms prevent transmission by reducing the risk that an exposure to HIV or STIs occurs during sex. Laboratory studies show that the materials used to make most condoms (such as nitrile, latex, polyurethane and polyisoprene) do not allow bacteria, viruses or other germs to pass through them. Therefore condoms act as a barrier to HIV and STI infection by preventing the mouth, vagina, penis and rectum from being exposed to:
Some condoms are made from a thin membrane of sheep intestine, also known as lambskin condoms. These condoms are not effective at reducing the risk of HIV or STI transmission because bacteria, viruses and other germs can pass through this membrane.
How Important Is It to Use Condoms Correctly and in What Ways Can They Be Used Incorrectly?
Incorrect use of condoms can compromise their effectiveness, thereby increasing the risk of HIV and STI transmission, even when they are used consistently. There are many ways condoms can be used incorrectly and research shows incorrect condom use is common.
Some types of incorrect use can cause condoms to break, slip or leak, thereby increasing the risk of HIV or STI transmission. This type of incorrect use includes using condoms that are too small or too large; using damaged or expired condoms; unrolling male condoms before putting them on; reusing condoms; not pinching the tip of the male condom when putting it on; using sharp objects to open condom packages; not using enough lubrication in combination with condoms; using oil-based lubrication with latex or polyisoprene condoms (oil-based lubrication is safe to use with nitrile and polyurethane condoms); or not holding the rim of the male condom when pulling out.
Other types of incorrect condom use can increase the risk of HIV or STI transmission even though the condom does not break, slip or leak. For example, some people may put a condom on late (after intercourse has started), remove the condom early (before ejaculation has occurred), or put the condom on inside out and then flip it over to use. These types of incorrect use can increase the risk of exposure to HIV and/or STIs.
Female condoms can fail in other ways that may increase the risk of HIV and STI transmission. For example, the erect penis can miss the outer ring and enter between the vaginal wall and the condom. It is also possible for the outer ring to be pushed, either partially or fully, into the vagina. These can all increase the risk of exposure to HIV and/or STIs.
How Effective Are Condoms at Preventing the Sexual Transmission of HIV and STIs?
The effectiveness of condoms depends on how consistently and correctly they are used. If condoms are not used consistently and correctly, then the risk of an exposure to, and transmission of, HIV and STIs increases.
HIV is transmitted through contact with fluids that contain HIV, including semen, vaginal fluid and rectal fluid. Research shows that male condoms can reduce the risk of HIV transmission when used for oral, vaginal and anal sex. The effectiveness of female condoms at reducing HIV transmission has not been directly studied.
Observational studies have investigated the effectiveness of male condoms in reducing the risk of HIV transmission between heterosexual serodiscordant couples (where one partner is HIV positive and the other is HIV negative). An analysis of these studies found that the rate of HIV transmission was 80% lower among couples who said they always used condoms compared to couples who said they never used condoms. Other studies suggest consistent use of male condoms provides a similar level of protection for gay men and other men who have sex with men.
There are several reasons why the level of protection in these studies may not reflect how effective condoms can be at reducing the risk of HIV transmission:
For these reasons, the effectiveness of condoms at reducing the risk of HIV transmission through oral, anal and vaginal sex is likely much higher than 80% when used consistently and correctly.
STIs can be transmitted in two ways. Gonorrhea, chlamydia and trichomoniasis are primarily transmitted through contact with infected fluids, such as semen, vaginal fluid and rectal fluid. Genital herpes (herpes simplex Type 2 or HSV-2), syphilis and genital warts (human papillomavirus or HPV) are primarily transmitted through contact with infected skin.
Several studies suggest male condoms can reduce, but not eliminate, the oral, vaginal and anal transmission of genital warts, genital herpes, syphilis, chlamydia, gonorrhea and trichomoniasis. However, other studies have found that condom use did not reduce the risk of STI transmission. These results were likely due to inconsistent and incorrect use of condoms among study participants.
Also, the effectiveness of condoms may depend on how the STI is transmitted. Condoms do not completely cover all parts of the body that can become infected, or are infected, by STIs that are primarily transmitted through skin-skin contact (such as herpes, syphilis and genital warts). Therefore, condoms may be less protective against these STIs compared to those that are transmitted through contact with infected fluids.
Studies suggest female condoms are equally effective as male condoms in reducing the vaginal transmission of STIs. Female condoms may provide more protection than male condoms against STIs transmitted through skin-skin contact. This is because they cover more parts of the body that can become infected, or are infected, by STIs.
This article was provided by Canadian AIDS Treatment Information Exchange. Visit CATIE's Web site to find out more about their activities, publications and services.
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