Sad study reveals how you can be monogamous and still get an STD

When my boyfriend and I started dating two years ago, we fell in love pretty instantly. I got on birth control faster than you can say “baby,” we both took an STD test—and then, like many exclusive lovebirds, we ditched the condoms.

Now I live in a safe little bubble where all my fears of contracting an STD have disappeared. This is because conventional wisdom tells me that if my boyfriend and I are both STD-free and only having sex with each other, we will remain in the clear.

But monogamy is not always perfect—and people do lie. This reality is the basis of a new study published in The Journal of Sexual Medicine, which compared the relative safety of monogamous relationships to open relationships (“consensually non-monogamous”) in terms of sexually transmitted diseases.

If you think you’re safe as a bonafide member of the monogamy club, you may want to think again.

For the study, Justin Lehmiller, director of the Social Psychology Graduate Program at Ball State University, recruited 556 participants aged 18 or older who were in relationships (351 monogamous and 205 consensually non-monogamous). Of the sample, 77.9% identified as heterosexual, 3.8% identified as gay/lesbian, 14.4% as bisexual, and 4.0% opted to write in their own identity.

Each participant was asked about his or her current relationship, past sexual experiences, condom use, and how often they were tested for sexually transmitted infections—as well as any additional sex partners outside of their primary partner.

They were also asked if their primary partner was aware they were having sex with other people. The point of all of these questions was to figure out if having more sexual partners—i.e., being involved in an open relationship—would increase one’s risk of contracting an STD.

It turns out it did not.

Despite having more lifetime sexual partners, people in open relationships were not any more likely to have an STD than those in monogamous relationships. Not only that, the people in open relationships were actually much safer about sex. They wore condoms with all their extra partners and got tested much more frequently. They were also less likely to lie to their primary partner about an extra-sexual dalliance.

For example, in the non-monogamous group, 72.4% of participants reported sexual involvement with someone other than their primary partner. Of those, 36.7% reported that their “primary partner did not have specific knowledge of this information.” So about a third of the sample wasn’t being totally upfront, but wasn’t technically breaking any relationship rules since they were in an open relationship.

In the monogamous group, on the other hand, 24.4% reported sexual involvement with someone other than their primary partner. Of those individuals, 75% reported that their primary partner did not have specific knowledge of this information. Almost all of them were keeping it a secret.

Not only that, people in the monogamous group were less likely to wear condoms with their side sex partner. Which makes sense—if you’re in an exclusive relationship and not using condoms ever, you might carry that practice over to extra sex partners as well. Combine that with less frequent STD testing, and suddenly, monogamy isn’t as fool-proof as we might have thought. This led Lehmiller to state in his paper:

The present findings reveal that monogamy is often implemented imperfectly. Persons who have made monogamy agreements often break them, and when they do, they are less likely to take safety precautions, get tested for STIs, and disclose those extradyadic encounters to their partners than persons who agree to some form of negotiated nonmonogamy … Thus, many people in monogamous relationships may not be as safe as they assume.

Lehmiller noted that the finding that one in four people in the monogamous group were cheating lines up with previous research on infidelity. “The potential danger of monogamy is that, if your partner puts you at risk by cheating, you’re unlikely to find out until it’s too late,” Lehmiller told me over email.

Finally, to cover all his bases, Lehmiller compared the STI rates of those in the monogamous group who actually remained monogamous to those in open relationships—and again, found no difference in prevalence of STIs.

“People in open relationships seem to take a lot of precautions to reduce their sexual health risks,” Lehmiller told me. “They have more open communication with their partners, a greater likelihood of using condoms with all of their partners, and higher rates of STI testing. Altogether, this means that open relationships aren’t as risky as people think.”

In conclusion—monogamy is not a guarantee, so continue getting tested. (Duly noted!) And just because someone chooses to be polyamorous doesn’t mean they also have herpes.

Taryn Hillin is Fusion’s love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn — not necessarily in that order.