Despite Americans' growing interest in consensually non-monogamous relationships, the vast majority of them agree to be monogamous with their partners. However, as we all know, a lot of people don't stay true to those agreements.

Indeed, cheating is widespread, with studies reliably finding that one-quarter to one-fifth of married people admit to having engaged in sexual infidelity at some point. Rates are even higher among unmarried college students, with somewhere between one-half and one-third saying they've cheated.


So what happens when one of these cheaters enters a new relationship? Are they at greater risk of cheating again? People have long assumed that this is the case—you know, "once a cheater, always a cheater." However, believe it or not, no one has ever studied this question scientifically—at least not until now. A new study published in the Archives of Sexual Behavior suggests that there's more than a hint of truth to this idea.

In this study, researchers examined data from a national US survey of young adults (aged 18 to 35) who answered questions about their romantic relationships at regular intervals over a five-year period. All participants were unmarried at the start of the study. Though nearly 1,300 people participated in total, the researchers focused only on the 484 adults who answered questions about at least two different relationships over the five years of the study.

During each wave of data collection, participants were asked whether they had ever had "sexual relations" with someone other than their partner since they began dating seriously. Over the course of the study 44 percent answered yes to this question at least once.

Participants were also asked whether their partners had done the same thing. In total, 30 percent knew that at least one of their partners had sex with someone else, while another 18 percent suspected this.

So did cheating in one relationship predict cheating in the next relationship? It sure did. In fact, cheaters were 3.4 times more likely to do so the next time around. However, serial cheating wasn't necessarily a forgone conclusion. Specifically, 45 percent of those who cheated in the first relationship did so in their next relationship; by contrast, among those who didn't cheat initially, 18 percent cheated with their next partner.


Interestingly, being cheated on in the first relationship predicted being cheated on in subsequent relationships, too. It's also worth noting that those who suspected their partners of cheating in one relationship were more likely to suspect their next partners of committing infidelity.

What this suggests is not only that there are serial cheaters, but also serial victims when it comes to infidelity.

While fascinating, there is an important limitation to this research, which is that the way these researchers assessed infidelity didn't distinguish between those who had sex outside of the relationship consensually vs. non-consensually. In other words, we don't know how many of these people were actually cheating and how many were in some kind of open relationship.

However, it's worth noting that the number of people involved in open relationships seems to be much lower than the number of people who engage in cheating. For example, a new nationally representative US survey found that the number of Americans in unfaithful relationships in the last year was 2.5 times higher than the number who said they were in open relationships.

So, when people in this study said they'd had sex outside of their relationship, odds are that they were cheating. As a result, even if we factored out the minority who were involved in open relationships, it probably wouldn't change the overall conclusions very much.


With that said, it's important to highlight that while about half of the supposed cheaters repeated their behavior the next time around, the other half didn't. This means that "once a cheater, always a cheater" definitely isn't true in all cases. It's a stereotype, to be sure. Consequently, it's not fair to judge someone as poor relationship material just because they've cheated in the past.

More important than whether someone cheated is why they did so. One of the most common reasons people cheat is because they aren't happy with their relationship. People who are driven to cheat by circumstance aren't necessarily bound to do it again as long as they find a partner they're more compatible with the next time around.

However, others don't necessarily cheat because of circumstance, but because of their personality. For instance, research has reliably found that infidelity is more common among those who have less care and concern for others and those who have less self-discipline (in other words, people who are low in the personality traits of agreeableness and conscientiousness, respectively). People with these traits are probably more inclined to cheat no matter what their relationship is like.

As you can see, when it comes to cheating, the past often—but not invariably—repeats itself. Whether infidelity becomes a serial behavior ultimately hinges on one's reasons for cheating in the first place.

Justin Lehmiller is the director of the social psychology program at Ball State University, a faculty affiliate of The Kinsey Institute, and author of the blog Sex and Psychology. Follow him on Twitter @JustinLehmiller__.