Infidelity is as old as monogamous relationships, and it tempts and plagues even the healthiest couples. Read on to discover 42 truths about a primal and mysterious human condition that has likely touched every relationship in one way or another.
42. Biologically Speaking
Of all the mammals on earth, only 3% are monogamous. Humans can count themselves among this group—for the most part. Interestingly, our closest genetic relatives, primates, are not monogamous.
41. Sudden Coital What?!
Men who cheat are more likely to suffer from a heart attack, or "sudden coital end," during the affair, as the man is usually in an unfamiliar setting and in a heightened emotional and physical state.
40. Definitely a Downside
Straight men with larger penises are actually more likely to be cheated on by their wives. In one study, for every inch Kenyan men had on their man's part, their likelihood of being cheated on rose by 150%.
39. I Listen to Everything but Rap and Country
In one survey, 42% of cheaters claimed that rock n' roll music was their favorite genre. Only 2% of rap fans, 3% of gospel fans, and 7% of classical music fans in the survey were cheaters.
38. Shopping Spree
Affair website Ashley Madison found that the most popular stores for cheating women who want to look good for their lover were J. Crew, Ann Taylor, and Macy's.
37. Side Benefits?
Cheaters often become more sexually active in their longterm relationship during their affair, taking advantage of the new spark in their sensual life.
36. Positive Reinforcement
The most common reasons for not cheating? Morality, the effects on any children from the union, the fear of remaining alone, and the effects on other people.
35. Deep Trouble
Male spouses who have deep voices are more likely to be suspected of cheating. The same is true for female spouses with high voices. 
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34. What a Flirt
When straight men flirt with other women, they become more intolerant of any transgressions by their partner. When straight women flirt with other men, however, they become more tolerant of slip-ups.
33. How About Them Odds
In over one third of marriages, one or both partners confess he or she has cheated.
32. Mars v Venus
22% of men have said that they have cheated on their significant other, while 14% of women have confessed to cheating on their significant other.
31. Once a Cheater, Always a Cheater?
Men and women who have been unfaithful before are 350% more inclined to cheat again than those who haven’t. Yikes. Talk about breaking a seal.
30. Just Getting Started
The most likely time for an affair to arise? Two years into marriage. This is around the time couples start to settle down, build a family, and forge a life together. In other words, it's a time where romance can take the back seat.
29. Out of Sight, Out of Mind
Business trips set the scene for infidelity to occur. About 35% of men and women admit to cheating on a partner while away for work.
28. Late Night Delivery
Overall, business is bad: common projects, late nights, and long hours spent together make it so that 85% of affairs start in the workplace.
27. Stay in School
Statistically, high school dropouts are more likely to be unfaithful.
26. Sugar Daddies Left Behind
Another vulnerable group are couples where one spouse is earning much less than the other spouse. Men who depend on their wives for financial support, in particular, are scientifically more likely to step out. 5% of financially dependent women cheat as opposed to 15% of financially dependent men.
25. More is Less
It's not all great for women looking for a Sugar Daddy, though. Although in general the more money men earn relative to their spouse, the less likely they are to be unfaithful, this stops once men reach the threshold of bringing in 70% of the household income. At this point, men become as likely to cheat as before.
24. More Money, No Problems
There's no downside for boss women: Women with a higher income bracket than their spouses are also less likely to stray and they are likely to remain equally faithful no matter what their income is relative to their spouses.
23. Lucky Number 9
Men whose ages end in the number 9 are the ones most actively seeking a little something-something on the side, particularly if they are about to turn 40 or 50. This could very well be their last chance to potentially have a romance outside of their relationship.
22. The Top Three
Desire. Love. Appreciation: These tend to be the traits that the “other woman” provides the cheating man that his wife, from his perspective, doesn't.
21. Your Stairwell or Mine?
Of the hospital cases of fractured penises, an estimated half of these injuries occurred during an extramarital affair. As with "sudden coital end," researchers theorize that this overrepresentation is a result of extra excitement while engaging in sensual positions, often in small and awkward places. No word on how many male cheaters suffered from fractured penises AND sudden coital end.
20. Difference of Opinion
When a woman cheats, it’s usually for emotional satisfaction, whereas when a man cheats, it’s usually from a physically emotional motivation. In perhaps telling results, men also believe sensual cheating is worse than emotional cheating, while women believe the opposite.
19. Sharing Isn’t Always Caring
People who cheat while in a monogamous relationship don’t typically wear condoms with their illicit lover, leading to higher rates of STIs.
18. Keep Your Loved Ones Close
Vasopressin, also know as the “cuddle hormone,” helps to form bonds with others. People with lower levels of vasopressin tend to trust people less–and are more likely to two-time.
17. Who's Your Daddy?
2%-3% of children are the result of infidelity. Furthermore, most of these children are raised without knowing that their father figures are not their biological fathers.
16. Happy Hump Day
Ashley Madison revealed that cheating happens the most on Wednesdays in the early evening. No, really.
15. Do Blondes Have More Fun?
Not factoring in dyed hair, 42% of blonde, 23% of redheaded, 20% of brown-haired, and 11% of black-haired women admit to cheating.
14. Or Do Brunettes Have More Fun?
This statistic, however, roughly switches for men: 40% of brown-haired, 23% of black-haired, 20% of blonde, and 5% of redheaded men admit to cheating.
13. For the Thrill of it
People with the “thrill-seeking” gene DRD4 have a higher risk of infidelity and promiscuity.
12. Blame it on Genetics
Even in happy, nurturing relationships, 56% of men and 34% of women are engaged in relationships on the side, suggesting that perhaps genetics play a more significant role than expected in infidelity.
11. More Than Meets the Eye
Cheaters tend to consider their significant others as more physcially attractive than their extramarital lovers.
10. Hook Up From the Palm of Your Hand
The iPhone is the device of choice among females in an affair. 64% of cheating women claim they would chat on their iPhone to their “mister-ess” in the same room as their spouse.
9. Get the One That Got Away
The advent of social networking sites has reconnected users with the old flings and missed connections of their past, resulting in more affairs and divorces.
8. Apples Don’t Fall Far
Men with fathers who are cheaters are more likely to stray than the son's of faithful men. This is likely due to a lethal convergence of both nature (genetics) and nurture.
7. Hazard of the Job
Males who are the most inclined to cheat work in finance, while females who are most inclined to cheat work in education.
6. Business is Booming
There are companies who provide cheating clients with “legitimate” alibis. Need a fake invitation or a cover story? The German company Perfect Alibi will come up with the perfect concoction.
5. The Danger of Being Caught
The guilt of an affair can weigh so heavily on a cheater's conscience that he or she may want to be found out. As Scott Haltzman, a clinical professor at Brown University, says, "Whether it's lipstick on the collar or emails left open on the family computer…it's a cry to say 'I need to get help.' Some people make it obvious because they want to stop but don't know how".
4. The Truth Hurts
Roughly 30-60% of all married individuals will engage in infidelity at some point during marriage—and that’s on the conservative side.
3. A Sign of the Times
More and more, people under the age of 30 are becoming disloyal. Why? More time spent away from spouses as well as the cultural habit of having multiple intercourse partners before marriage.
2. Survival of the Species
Women are more likely to stray from their partners when ovulating, i.e. when they are most fertile. The exception? A heterosexual woman is much less likely to have an affair--at all times-- if her man is attractive.
1. A New Hope
It is possible to repair your relationship after infidelity, but research suggest the the only way this is possible--according to family counsellor M. Gary Neuman--is if the unfaithful party feels remorse. Additionally, the cheated party has to trust the cheater and believe the affair has completely ended, and the victim should stay away from sensitive questions about the affair.
