Can Anal Sex Affect the Vaginal Microbiome?

Highlights from this article: 

• If you have vaginal sex directly after anal sex with no barrier method (i.e. a condom), there is a chance that disruptive pathogens from your anal microbiome can cause an infection in your vagina
• Barrier methods, cleaning up between vaginal and anal sex, and washing sex toys can all help to decrease the chance of mixing microbiomes. 
• Initial research shows a correlation between anal sex and BV, yeast infections, and UTIs, but more research is needed to determine how causal the relationship is. 
• Many STIs can be transmitted through anal sex.

At Evvy, we spend a lot of time talking about the vaginal microbiome, the complex ecosystem of microorganisms that lives inside the vagina. Vaginas aren’t the only part of the body that hosts microbes. Your gut is also home to the trillions of bacteria, yeast, and viruses, aka your gut microbiome. While your gut microbiome is essential to your overall health, including your vaginal health, it can also be home to pathogens that can potentially infect your vagina. 

There are a few ways the gut and vaginal microbiome interact with each other, but some of our own activities can also play a role—including the more pleasurable ones. That’s right, we’re talking about anal sex. 

So you might be wondering, will having anal sex give me a vaginal infection?

Here we break down what we know about the connection between anal sex and the vaginal microbiome. 

How does anal sex affect the vaginal microbiome? 

Like the vagina, the anus (or rectum) has its own resident microbiome. The anal microbiome can be influenced by your diet, genetics, and your lifestyle. 

There are relatively few studies on sexual practices like anal sex and how they influence the vaginal microbiome. Here’s what we do know: when switching to vaginal sex directly after anal sex, there is a possibility of carrying over of microbes from the anus to the vagina. 

There are a few ways to minimize the mixing of microbes: 

• Use a barrier method and change the barrier for different activities (i.e. switching to a fresh condom) before inserting anything into the vagina. 
• If you aren’t using a barrier method, having your partner wash their penis and/or hands can make a big difference. If a shower is going to disrupt your rhythm, try keeping some baby wipes next to the bed for easy clean-up. (Not feminine hygiene wipes, which can be a horror show for your vaginal microbiome. Fragrance-free is best!)
• Don’t transfer lubricant from the anus to the vagina.
• Washing sex toys when using them on a new body part (as well as a different person). 

If you’re only having anal sex and not having vaginal sex in the same session, it’s unlikely for you to influence the vaginal microbiome, especially if you are using lubricant that is microbiome-friendly. 

Let’s say you do switch from anal sex to vaginal sex without any barriers or clean-up (we get it, things happen!), could this cause Bacterial Vaginosis (BV), a yeast infection, or a UTI? Read on to see what the research says. 

Anal sex and vaginal infections

Can anal sex cause BV?

One study published in 2008 found an association between BV and vaginal intercourse immediately after receptive anal intercourse, showing that the carry over of microbiomes from the anus into the vagina may play a role in vaginal dysbiosis (aka an imbalance of disruptive bacteria in your vagina). Again, using a new condom greatly reduces this risk! 

Can anal sex cause a yeast infection?

A 1995 study of risk factors for vaginal yeast infection found that receptive anal sex was a risk factor for developing a yeast infection. A second study, published in 2005, also found that receptive anal sex was a potential risk factor for developing a vaginal yeast infection. It’s worth noting that this type of clinical study showed a correlation between yeast infection and anal sex, but doesn’t say that anal sex definitively caused a yeast infection for participants. 

Can anal sex cause a UTI?

Research on UTIs and anal sex is very limited. There is one case study which followed two patients with UTIs that suggested receptive anal intercourse can be associated with UTIs. However, two is a small sample size. We need a study with many more participants to be able to say definitely that anal sex is associated with UTIs. (Just another topic to add to the list of research questions we need to address to close the gender health gap.) 

Can I get an STI from having anal sex?

While research is spotty on the association between anal sex and some vaginal infections, we know for certain that you can get an STI from anal sex. Many STIs can be transmitted through multiple types of sexual activity, including anal sex. Depending on the type of STI, it’s also possible to develop symptoms in the rectal region. 

For example, HIV, which infects immune cells all over the body, is frequently transmitted by unprotected anal sex. One study published in 2018 found that some women with chlamydia or gonorrhea infections had the infection-causing bacteria in both their genital and rectal microbiomes, suggesting they can be transmitted between the two sites. 

What else should I know about anal sex? 

Since we know there is a very good chance that your high school sex ed class didn’t cover this, we put together a few other helpful booty basics to keep in your back pocket (wink, wink): 

• Lube is your anal sex bff! Unlike the vagina, the anus does not self-lubricate. Using lube will not only make anal sex feel good, but also prevent anal fissures (aka tiny tears on the anus, ouch).  
• Start small. Fingers are a great first introduction to anal play, as well as stimulating the outside of the anus with touch or a vibrator. Many people find it overwhelming to insert a penis or large toy if they’ve never had anal sex before, so go slow. 
• It shouldn’t hurt. It’s a myth that anal sex has to be painful. Pain is your body’s way of saying something doesn’t feel quite right, so listen to it! You may need more lube or to slow down. It’s also best to steer clear of numbing creams. Not being able to feel your body’s pain signals can lead to injuries. 

Anal sex is not only for people of certain genders or sexualities. People of all identities can experience pleasurable anal play. The anus has a ton of nerve endings (not as many as the clitoris, but still quite a few!) that makes anal sex feel good on any body. Of course, if it’s not your thing, that’s OK too!

Whether the culprit was anal sex or not, an Evvy test can help to tell you about what’s happening in your vaginal microbiome if you’re experiencing any pain, itching, or other unpleasant symptoms.

While we definitely see some areas of opportunity to learn more about the relationship between anal sex and the vaginal microbiome, the evidence we do have shows that it’s worth being mindful in the bedroom. The extra steps of adding a barrier method and cleaning up in between activities could save you from some uncomfortable symptoms down the road!

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Published on December 7th, 2022.