One in four married adults in the US have cheated on their spouse, a survey by MSNBC.com and iVillage has revealed.
The Lust, Love and Loyalty survey talked to people about their attitudes to and experiences of cheating.
It found that 81 per cent of women and 62 per cent of men thought that cheating was not acceptable under any circumstances.
Divisions about the definition of cheating were found to vary between the sexes.
While both men and women generally agree that physical contact and kissing constitute cheating, 43 per cent of men and 33 per cent of women do not believe online sexual talking and Webcamming count as infidelities.
Friends were found to be the most common cheating partners, in 40 per cent of cases and co-workers come a close second scoring 35 per cent.
Affairs were found to generally be short-lived, with 29 per cent ending after a week and 47 per cent after a month.
But people are worrying too much about cheating, according to Julia Somerfeld, senior health editor of msnbc.com.
She said: "The good news is that most of us fear cheating more than we really need to. People overestimate the rate of cheating by nearly double.
"Perhaps that's because we're deluged with images of cheating at the movies and in celebrity magazines. We think if Reese Witherspoon and Sienna Miller are getting cheated on, who's safe?"