Regretting a one night stand does not stop people from having the romantic encounter again, research suggests.
Remorse over a one-time fling was thought to help protect our wellbeing, with sexual regrets potentially prompting people to change their behaviour, warding off infections and even physical danger.
To learn more, scientists from the Norwegian University of Science and Technology had hundreds of students complete a questionnaire on intimacy twice, around four months apart.
Results reveal those who regretted having casual sex did not then change their behaviour.
More than 500 students – aged 18 to 30 – completed the questionnaire the first time round, of whom over 280 filled it out again several months later.
They were asked whether they had ever had casual sex with someone or turned down the opportunity, as well as how they felt about their action – neutral, regret it "somewhat" or regret it "very much".
The results suggest the participants who regretted having casual sex around the time of the first questionnaire were no less likely to have repeated the activity by the time they filled out the survey again.
"For the most part, people continue with the same sexual behaviour and the same level of regret," said study author Professor Leif Edward Ottesen Kennair.
Remorse was more common among those who endured "sexual disgust", but lower in those who felt "gratified", "took the initiative" or had a "sexy partner", the scientists revealed in the journal Evolutionary Psychology.
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Regretting a one night stand was also linked to lower odds of entering a committed relationship down the line.
This may be surprising, considering regret was thought to have evolved to alter a person's behaviour.
"A lot of emotions are functional, like disgust protects against infection and fear protects against danger," said Prof Kennair.
Why people may not "learn" from their so-called "mistake" could come down to the individual's personality.
"If regret helped, would not most sinners eventually become saints?" said Prof Kennair. "What do you regret the most often? Has it changed your behaviour?"
The results further suggest the female participants regretted having casual sex more than the males, while the latter were more likely to lament turning down the romantic encounter.
So-called "inaction regret" – refusing casual sex – was not linked to "increased short-term sexual activity" for either the male or female participants.
When it comes to the differences between the men's and women's regrets, the scientists wondered if the "modern mating scene is evolutionary mismatched".
A person's emotional response, like remorse, may also "exist despite not being functional". Ruminating over problems, for example, does not generally solve the issue, the scientists pointed out.
The NHS recommends people use condoms to ward off unwanted pregnancies and sexually-transmitted infections (STIs) during vaginal intercourse. The contraception also helps prevent STIs during anal and oral sex.
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