"Once a cheater, always a cheater" may well be based on truth. Stokkete / Shutterstock Admitting you were unfaithful in past relationships is a gamble. "Once a cheater, always a cheater" is a phrase that can damage your reputation for a long time, if you're unlucky.

According to some scientific research, there could actually be some fact behind the idiom.

A new study, published in the journal Archives of Sexual Behavior, followed 484 participants in mixed gender romantic relationships. The researchers asked the participants to report their own "extra-dyadic sexual involvement" — having sexual relations with someone other than their partner — and also whether they had suspected their partners of infidelity in each romantic relationship they had been in.

The results showed that people who had messed around in their first relationship were three times more likely to cheat in their next relationship compared to those who had stayed faithful.

Those who knew that their previous partners had cheated on them were twice as likely to have their next partners do the dirty on them too. Suspicion also appeared to be hard to shake, as people who suspected their first relationship partners of cheating were four times more likely to report suspicion in later relationships.

One reason for this could be the fact that when we lie, our brain actually gets used to it. This was the finding of a study published in Nature Neuroscience, which showed that telling small lies desensitizes our brains to the associated negative emotions, which may encourage us to tell bigger lies in the future.

In other words, those little white lies we tell all the time might build up into bigger, more serious untruths.

In the study, participants were divided into pairs. One was shown a glass jar full of coins, and the other a blurry picture of the same jar. The participant with the jar was instructed to help their partner guess how many coins it contained.

One group of participants were told they would get a cash prize if their partner overestimated the number of coins, leading them to lie and exaggerate. The researchers saw that the amygdala — the area of the brain responsible for emotions — responded when participants lied, but this response weakened when lies were repeatedly told.

A similar thing could happen when somebody cheats on their partner. The first time they do it, they will probably feel terrible. However, if it happens again, they will feel slightly less bad, and so on. It could all be down to the biology of the brain, and what the amygdala is making you feel.

In an interview with Elite Daily, researcher at Princeton Neuroscience and co-author of the study Neil Garrett said: "What our study and others suggest is a powerful factor that prevents us from cheating is our emotional reaction to it, how bad we feel essentially, and the process of adaptation reduces this reaction, thereby allowing us to cheat more."

"With serial cheaters, it could be the case that they initially felt bad about cheating, but have cheated so much they've adapted to their ways and simply don't feel bad about cheating any more."

He added: "Another possibility is that they never felt bad about cheating to begin with, so they didn't need adaptation to occur, they were comfortable with it from the get-go."