New research suggests cheating men can be spotted by the shape of their face.
Experts found men with more "masculine" faces are more likely to be viewed as unfaithful - and these men also self-reported they were more likely to cheat.
However, researchers recommended their results be taken with a grain of salt. After all, we all know judging a book by its cover is wrong.
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The study was comprised of 765 men and women, who were asked to judge the facial features of 189 white adults who had been photographed.
They were then asked to rate how faithful they thought each person was on a scale of one to ten. Men and women rated cheaters higher on the scale - showing unfaithfulness can be seen in male faces. However, there was no such effect on female faces.
Writing in the Royal Society Open Science journal, researchers said suspicion arising from men with masculine features - such as a strong brow and jawline, and thinner lips could have offered an evolutionary advantage.
Heterosexual women would spot an untrustworthy partner, and men would recognise a man who was a threat.
Women are able to pick out cheating men, but the results from men trying to pick out cheating women are much weaker, according to the study.
This could be because women are less prone to cheating than men, or because some women wear makeup, and therefore mask aspects of their facial features.
Researchers concluded further experiments, with a wider range of people photographed, were necessary for conclusive answers.