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I need to better understand how condoms can protect me from STIs.

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fox asks:

I'm unclear on how condoms are supposed to be effective in preventing female-to-male contamination during "plain" sex, I mean insertion of the penis into the vagina. Let me explain.

Latex is an effective barrier to virii and germs. I get that. As far as protecting the woman is concerned, I've no trouble believing it works. The STD virii or germs are present in the semen and/or pre-cum; these are "emprisoned" by the condom, don't get out, and don't get into contact with any part of the anatomy of the woman. She's protected. The sweat of the man does not contain these virii or germs and thus no risk with the rest of the skin-to-skin contact. But in the other direction, I don't quite get it.

Heather Corinna replies:

Fox's question continued:

From what I understand, when a woman gets sexually excited, she secretes some kind of lubrication in her vagina. I presume that for STDs, the virus / germ is present in that natural lubricant, and that the contact with that lubricant is what's dangerous. But a condom covers only the shaft of the penis. Couldn't the lubrication "drip" out a bit and land on the man's crotch area, not covered by the condom? And here you are, infection! Or, similarly, your article here says that vaginal discharge / secretions will end up on the woman's labia; when thrusting "till the end", penis shaft completely inserted, wouldn't these labia come into contact with the men's uncovered crotch and, again, infect him?

If my premise is wrong and vaginal discharge/lubrification does not contain the STD virii/germs, then how does STD transmission from woman to man (during unprotected sex) happen in the first place?

In the early 80's, safer sex was called safe sex. That language was changed to reflect the knowledge that these practices -- namely, latex barrier use, STI testing and limiting the number of sexual partners -- couldn't make sex "safe." They could only make sex safer. So, know above and beyond all else that what condoms can do is reduce our risks: they cannot eradicate them nor provide absolute protection, ever. They make sex safer for us and for our partners: they don't make sex safe.

Not all men and not all women have the same kinds of bodies or genitals. Some people who identify as men have a vulva. Some people who identify as women have a penis. But for the purpose of your question, when I say "men" here I will mean people with a penis, and when I say "women" I'll mean people with a vagina, especially since the studies I'll be talking about use that same language, and I don't want to confuse you instead of helping you get more clear.

Let's start with some STI (sexually transmitted infection) basics. While STIs tend to differ in a lot of ways -- some are parasites, some viruses, some bacteria, some are more easily transmitted than others -- on the whole, we divide them into two basic groups: those transmitted by fluids, like HIV, gonorrhea, chlamydia and trichomoniasis, and those transmitted just by bodily contact, like HPV, herpes, syphilis, molluscum, chancroid and scabies.

With fluid-borne infections, infection occurs not because fluids have contact with skin like that on the thighs or testes, but with parts of the body which can or do provide a direct route to the bloodstream. So, for instance, in vaginal intercourse, your sexual fluids, and any infections they may be carrying, can or do reach the inside of the vagina, the cervix, the uterus and beyond: all places with direct routes to the bloodstream. On a female partner's part in intercourse, her fluids, any any infections she's got, could reach your urethra, which is often the only direct route into the bloodstream through the penis, particularly for men who are circumcised (uncircumcised men may have higher risks than men who are not). For men and women alike, other pathways to the bloodstream that can be other possible routes of fluid-borne infection are the anus, the mouth, and any shaving cuts or other skin abrasions or wounds on the body, including on or inside the genitals. Unless you have a cut or abrasion on the base of your penis, testicles or "crotch area," these are not going to be sites for fluid-borne infection transmission. If we're only talking vaginal intercourse, the anus is a non-issue.

You're asking specifically about how you'd be protected during vaginal intercourse with condoms: the simplest answer is that condoms cover the opening of your urethra completely, the orifice through which you would be most likely to acquire a fluid-borne infection with that activity. So, the answer for the most part is that you'd be protected very well, especially from fluid-borne infections.

However, not all sexually transmitted infections are transmitted by body fluids. Some infections spread by only contact between or to mucous membranes like genital tissue, the mouth, the inside of our noses. Fluids are a non-issue with these kinds of infections. Condoms reduce risks of STI transmission for these kinds of infections well, well, but not as well as they can reduce risks of fluid-borne infections, primarily because condoms, dental dams or latex gloves often don't provide a barrier to the whole genital or oral area. These are the infections to figure you, as person with a penis, have less protection from when using condoms.

When you're expressly asking about penis-in-vagina intercourse, women tend to be a lot more susceptible to acquiring most infections than men. That's because of physiological differences and also because of common social/gender inequities that often impact women's health, like men as a group being tested less often for STIs, having sex more often outside relationships understood to be monogamous and more frequent refusal to use condoms. If you spend time with studies on latex barrier use and STIs, one common finding you'll see is that men are frequently afforded better protection from condoms with most infections than women are. That does not mean you shouldn't be concerned about your own health: you so should! I encourage everyone to protect themselves as best they can. However, I think it's also important to just know, in having the facts, that female partners you have for intercourse will usually be at a higher risk than you will of acquiring an infection.

Another having-the-facts riff: women can and often do produce several different fluids. Self-lubrication from arousal, menstrual fluids, and fluids produced by the cervix and the vagina that are part of the fertility cycle and/or the way the vagina keeps itself clean are all typical. Some women also ejaculate. For men, the genital fluids at play are ejaculate and/or pre-ejaculate, and any fluids/oils produced by the foreskin if you have one. Both your bodies produce urine and fecal matter, and both of you have blood. Nursing or lactating women also produce breast milk. With fluid-borne infections, the fluids which typically transmit STIs are primarily vaginal fluids, penile fluids, blood and/or breast milk. Fecal matter is another biggie in terms of bacterial infections and hepatitis, but that's not something you or a partner are likely to be exposed to with vaginal intercourse.

So, just how effective ARE condoms for you per infections? If you read public health information, you will most typically see them stated as "highly effective," which we know them to be. Reliably expressing just how highly effective in numbers is harder to do outside any one specific study.

With fluid-borne infections, condoms have typically been found in studies to reduce the risk of infection by as much as 99%, and as little as around 50%, with both figures largely influenced by how consistently and correctly condoms are used. With skin-to-skin infections, findings for protection range from around 30% to around 90%. Again, proper use and consistency is a factor. Specifically addressing HIV protection, the UNFPA states an effectiveness rate of 90-96%. The CDC does not tend to state mathematical figures, but instead say that "consistent condom use is highly effective in preventing HIV transmission."

That substantially lower rate of protection listed for infections like HPV and Herpes is because of what you said about how condoms do not completely cover the genital area, just not because of contact with fluids, as those infections don't require fluids for transmission. Here's what the CDC has to say on that, "Correct and consistent use of latex condoms can reduce the risk of genital herpes, syphilis, and chancroid only when the infected area or site of potential exposure is protected. While the effect of condoms in preventing human papillomavirus infection is unknown, condom use has been associated with a lower rate of cervical cancer, an HPV-associated disease." For the record, the female condom covers the vulva more than male condoms, so it is currently being studied to see if it provides better protection against infections like Herpes and HPV. It might, it might not. We don't know yet.

Some of the language I'm using is imprecise, and I know how frustrating that is. I'd like one easy, firm number as much as the next guy. But because the effectiveness condoms may or do provide at reducing the risk of infection varies a good deal from infection to infection, person to person and from area to area, based on a lot of different factors, we can really only give broader estimates. Around ten years ago, the NIH did an extensive review of 138 peer-reviewed articles on condom effectiveness per infection and disease. That review found that 90% of the studies done demonstrating condom effectiveness per STIs were sound. You can access that review here, and if you want to look at the range of what each of the studies found -- not all on the same infections, but on a range of different infections -- you can take a peek at page 3 of the report, which offers an excellent chart of the findings.

The CDC also addresses this factual mushiness when they say, "Accurately estimating the effectiveness of condoms for prevention of STDs is methodologically challenging. Well-designed studies address key factors such as the extent to which condom use has been consistent and correct and whether infection identified is incident (i.e. new) or prevalent (i.e. pre-existing). Of particular importance, the study design should assure that the population being evaluated has documented exposure to the STD of interest during the period that condom use is being assessed. Although consistent and correct use of condoms is inherently difficult to measure, because such studies would involve observations of private behaviors, several published studies have demonstrated that failure to measure these factors properly tends to result in underestimation of condom effectiveness." One of the toughest parts of determining condom effectiveness in study is how very often people do not use them consistently and correctly, and figuring out when and if they actually have. No one is watching people every time they have sex in these studies to find out if they really are or are not using condoms, or to check for correct use.

Consistent -- as in, you always use 'em -- and correct -- as in, you use quality condoms properly -- use of condoms is a super-duper big deal. For example, this study on men and gonorrhea showed that men who did not use condoms consistently or correctly had more than a 90% risk of contracting the infection than those who did use them consistently and correctly. This study on HPV transmission showed that "the incidence of genital HPV infection was 37.8 per 100 patient-years at risk among women whose partners used condoms for all instances of intercourse during the eight months before testing, as compared with 89.3 per 100 patient-years at risk in women whose partners used condoms less than 5 percent of the time."

However difficult it can be to quantify this in clear numbers, consistent and correct use of condoms greatly reduces the risk of sexually transmitted infections. That's something people in public health can and do say with certainty, and from a medical/health standpoint, that's not in question. We can also say with certainty that men are generally at a lower risk of STI acquisition than women when it comes to vaginal intercourse, and that it's most sound to be concerned with the way you are using condoms -- Are you using them every time? Are you using them properly? -- rather than if condoms can or can't work: we know they can, and that they are a lot more likely to prevent infection with proper, consistent use.

If you are going to engage in sex with others, there are three parts of safer sex practice we know make a profound difference in the spread of infection and disease: consistent and correct latex barrier use, regular STI testing and limiting the number of sexual partners. Just any one of those things can reduce risks, though with testing, that can only help if and when it is paired both with treatment of any STIs that can be treated, and with adjusted behaviors on the part of anyone infected like using condoms, informing partners (so they can also be treated or choose not to have sex), and/or making choices not to have sex, particularly during treatment or if an infection is not treatable. If we want to be sexually active and reduce our risks as best we can, ideally, we've got to do all three parts of those practices, not just one, like only using condoms.

Anyone who wants to have absolutely NO risks of sexually transmitted infections, will need to opt out of ANY of the kinds of sex where transmission can occur.

Something we often find with Scarleteen users is that while so many are great about condom use, fewer are so great about talking to partners about STIs; asking about a partner's status, disclosing their own or insisting on testing for partners and getting regularly tested themselves. That's a big, big piece of prevention missing. So, I encourage you to talk about testing. If either you or a current or potential partner have not been tested or aren't getting regularly tested, step it up and ask they do. Make sure you're doing your own part by getting your own tests. It's something you can do together, or can offer to keep a partner company while they do, if you already have had your own recent screenings. People can feel pretty scared about testing, especially if they aren't already in the habit of going, and having someone to provide emotional support can make a huge difference. Should you ever have a potential partner who refuses to be tested, my best advice is to just nix sex with that partner. Should you refuse testing, I'd give any potential partner of yours the same advice. As well, I'm a big fan of encouraging people with sex to do our best to think of everyone involved: of both what best protects us and our partners. Partnered sex is something where we're supposed to be thinking about everyone involved, not just ourselves, and safety in that is no exception.

You should also know that most infections, so long as they are quickly diagnosed and quickly and effectively treated, do not pose giant health risks to most people. A lot of the scary things said about some infections are fears we inherited from times past when we did not know how to test or have the ability to, or did not have access to treatment or effective treatments like we do today for so many infections, or from propaganda that is not in alignment with what scientists, doctors and other people working in public health with STIs know.

HIV is not in that group, because we do not yet have medicines which can rid the body of HIV infection like we do for infections like chlamydia or gonhorrhea. HPV and herpes are also exceptions, but for otherwise healthy people, when HPV infections are not those associated with cancers, there, too, are often benign infections. So, again, testing is such a big deal, and so is treatment: people who work in infectious disease who you talk to about this will generally agree that our biggest challenges to reducing STIs are a) all people using barriers consistently and correctly, and b) all people having access to testing and treatment and getting testing and treatment.

You can always ask your sexual healthcare provider the same sorts of questions you're asking me. A lot of folks don't realize that it's not just their job to take care of your body and your health, it's also their job to provide patient education. As a sexuality and sexual health educator, I benefit incredibly by talking to providers about all of this, a skill and a practice that is just as important for all of us as patients.

Here are a few extra links to help you out:

This piece was reviewed by Joanna Dawson, MPH, United Action for Youth

written 11 Aug 2010 . updated 27 Jan 2014

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