Most people have always assumed that it's men - because of their testosterone. But the reality is, about 1-in-5 spouses cheat, and these days, husbands and wives cheat in equal amounts. Now, some experts say we should take these results with a grain of salt - because if cheaters are lying to their spouse, then they're probably also lying on surveys! But the trend that all of these studies makes clear is that when it comes to being unfaithful, women are "catching up" to men. In fact, psychologists are reporting more cases where married women are openly and actively seeking out affairs! So, the real question is why? And what's changed? * There's the "opportunity factor." In other words, there are far more women with jobs than there were a generation ago - which means women have more chances to work late, travel, and interact with other men. So, that may be creating more temptation to cheat. * There's our online social networks, like Facebook. They make it easier than ever to connect with old flames, or new friends. And experts say online, emotional affairs can be just as devastating to a relationship. * Some women say they cheat for the same reasons men do. To boost their ego, validate their attractiveness, or feel more appreciated. * But there's also what psychologists call "infidelity overload." Meaning we're seeing more TV shows and movies where the plot makes it look like cheating is inevitable in relationships. So, that may be sending the message to more women that infidelity is acceptable. A whopping 86% of men and women say they still value monogamy in a relationship, and that infidelity is a deal-breaker.