Ever wonder what keeps some people faithful while others are spreading their cooties all around town? Well, there's more to monogamy than sheer willpower, according to new research.

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In a study published in the Personality and Social Psychology Bulletin, scientists recruited nearly 250 heterosexual people and had them rate the attractiveness of members of the opposite sex…all in the name of science.

In one experiment, people were shown a pic of someone of the opposite sex, as well as a profile that included whether they were single or in a relationship. People who were in a relationship tended to say that single people (who might be a "threat to their relationship," according to the study) were less attractive than other single people deemed them.  

In a second experiment, people were asked to report how satisfied they were in their relationship before ranking the attractiveness of others. People who said they were happy with their S.O. once again ranked single folks as less attractive. But, those who weren’t all that satisfied in their relationship were more likely to say those singles were lookin' mighty fine. 

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While this is super interesting, what does it mean? Scientists say that when we’re happy in a relationship, we want to keep things that way. As a result, we unconsciously downgrade the looks of other people in our minds so that they don’t tempt us to cheat.

Of course, there’s a huge difference between thinking someone is hot and actually stepping out on your S.O., and it’s totally possible to think Zac Efron is sexy while still being into your guy (ahem, just saying...).

This article originally appeared on WomensHealthMag.com.