Being in a serious relationship has a lot of perks, but protection from sexually transmitted diseases (STDs) may not be one of them. According to a recent study, couples in monogamous relationships are just as likely to get an STD than those who openly have multiple sexual partners. The reason for this surprising conclusion? Infidelity.

According to the Just World Theory, in order to help our minds comprehend the vast injustices we witness on nearly an everyday basis, we victim blame. Rape victims probably drank too much. Getting mugged means you didn’t keep a close eye on your belongings. And, of course, only promiscuous people get STDs. However, a recent study now published in the Journal for Sexual Health examined the sexual history of 556 adult participants, and found that, like other instances of victim blaming, this just isn’t true.

Of the 556 volunteers involved in the study, 351 were in a monogamous relationship and 205 were in consensual, non-monogamous “open” relationships — meaning they had one main sex partner but still slept with other people. The volunteers were asked various questions on their sex life, including, lifetime number of partners, whether they were faithful, if their partners knew about their infidelities, how often they used condoms, STD history, and how often they got tested for STDs.

Results revealed that there was no measurable difference in STD rates among individuals in monogamous relationships and those in open relationships. Although the numbers themselves could not explain why people who only slept with one person at a time had the same rate of STDs as those who openly slept with many people, the volunteers' sexual history gave a clue.

Individuals in monogamous relationships reported using condoms less and getting fewer STD check-ups than those in open relationships. In a perfect model of monogamy, this would be fine, but, unfortunately, humans are anything but perfect. About a quarter of the individuals in monogamous relationships also admitted to cheating, but 75 percent reported that their partners had no idea of their infidelity. On the other hand, while 72 percent of those in open relationships admitted to sleeping with someone other than their main partner, only 36 percent reported that their partner was unaware of their external sexual activity.

“The present findings reveal that monogamy is often implemented imperfectly,” wrote lead researcher Justin Lehmiller, as reported by Fusion. “Persons who have made monogamy agreements often break them, and when they do, they are less likely to take safety precautions, get tested for STDs … Thus, many people in monogamous relationships may not be as safe as they assume.”

So, even though those in open relationships were having more sex with more people, they are doing it in a safe way and the precautions they took meant their STD rates are on the same level as seen in imperfect examples of monogamy, aka marriage.

Source: Lehmiller JJ. A Comparison of Sexual Health History and Practices among Monogamous and Consensually Nonmonogamous Sexual Partners. The Journal of Sexual Medicine. 2015.