Loved-up couples may see other people as less attractive than they really are, according to a new study that appears in the journal Personality and Social Psychology Bulletin. The researchers behind the project suggest that this apparent inability to recognize the beauty of others could be part of a subconscious defence mechanism that stops partners from cheating on one another.

On paper, monogamy should be a pretty easy game to play – after all, there’s only one golden rule you have to follow in order to do it right. Yet as the Ashley Madison scandal highlighted, there are plenty of people out there who find being faithful to just one partner a bit of a stretch. This raises the question: Why do some couples crumble under the temptation of illicit liaisons with outsiders while others live happily ever after?

To investigate, researchers recruited a number of volunteers to take part in an experiment. Some of these participants were single while others were in a relationship. Those that were off the market were then asked to answer a number of questions designed to evaluate how happy they were with their partner.

All participants were then shown a series of pictures of faces of the opposite sex, while also being told whether the people they were looking at was single or in a relationship, and if single, whether they were currently on the lookout for love.  

Each picture was then followed by 11 more images of the same face, 10 of which had been distorted to varying degrees in order to make it either more or less attractive. This was achieved by tinkering with aspects such as symmetry, which has been shown in a number of studies to be a key indicator of facial attractiveness.

Participants were then asked to identify which of the 11 faces was genuine. Interestingly, results showed that people in relationships consistently picked an “uglier” face than single participants. Even more intriguing, this effect was more noticeable among those who were happiest in their relationships, and also when the people in the pictures were said to be both single and on the hunt for a lover.

^{People who were less happy in their relationship were more likely to find others attractive. Antonio Guillem/Shutterstock}

Discussing this finding, the researchers believe this “perceptual downgrading effect” occurs “outside of individuals’ conscious awareness,” and helps to eliminate the threat posed by dangerously attractive alternative partners to their love life.

Exactly how this occurs is something the study authors cannot answer at this stage, although one potential explanation could reside in the previously-established idea that people who are romantically committed pay less attention to the more beautiful characteristics of people that aren't their partners.

Extrapolating from their study, the researchers suggest the same mechanisms may be at work in a range of non-romantic scenarios that require self-control – such as resisting food or the urge to play in the sunshine when we have more important work to do.