Picture an adulterer and who do you see? There's a high chance you're thinking of a middle-aged man, perhaps with a history of broken marriages.
This might be the popular image of someone who cheats but, as a psychiatrist with two decades' experience in treating sexual issues, I can tell you that the profile of a modern adulterer is much more complex and nuanced.
For one thing, while men are having affairs at the same rate as they've done for the past two decades, today a cheater is more likely than ever before to be female. There's a good chance that he or she will be a high earner, aged between 40 and 60. However, affairs are also increasingly prevalent among the younger and, perhaps more surprisingly, the older generation, reports Daily Mail.
Yet, strange as it sounds, it's quite possible today's adulterer is happily married. In recent surveys, more than a third of cheating women and half of cheating men say they are perfectly content with their long-term relationships — but cheat anyway.
While we would all like to think we'd never cheat, it's not an isolated activity confined to a few essentially "unfaithful" people.
In simple terms, we become more likely to cheat if we are given the opportunity — and modern life is giving us more and more opportunity.
Indeed, I believe seismic sexual shifts in society are remodelling the landscape of infidelity. This is especially true for women, whose attitudes have undergone the most radical change as they have gained social and sexual freedom.
Women used to be cruelly cast out for having extra-marital affairs. Literature tells stories of "fallen women", such as Hester Prynne (in Nathaniel Hawthorne's novel The Scarlet Letter, she's forced to wear a red A for "adultery"), Anna Karenina and Madame Bovary, who suffered greatly for their sexual and romantic desires.
Yet women are now more than levelling the playing field with men over breaking marital bonds.
Even a few decades ago, women cheated only half as often as men. One highly respected study reveals that while the number of married men who have ever cheated remained stable at around 20 per cent from 1993 through to 2016, among women of all ages there is a definite upward trend.
In 1993, just 10 per cent of women admitted to cheating. Now, the figure is 15.4 per cent — roughly a 50 per cent increase. A different poll suggests women have virtually caught up with men, with 19 per cent cheating.
The most likely cause of this startling increase in infidelity among women is their long overdue economic and social emancipation — which provides more opportunities to cheat in the workplace and means women have become less reliant on men for financial support.
And, while disapproval rates of infidelity are actually higher now than they were in the Seventies, women no longer face the stigma that once surrounded adultery.
Surprisingly, well-paid and highly educated women are significantly more likely to cheat. Research confirms that's especially true for university-educated women and those who earn more than £55,000 — particularly if that's more than their husband's salary.
Why? No one can say for certain, but it may be, in part, because they feel less pressured to make bad relationships work. University-educated women are also the most likely group to instigate divorce, suggesting they feel more empowered to leave a marriage whether or not cheating has occurred.
And the trend for women to have more affairs seems only to be growing among the younger generation. Research into the sexual activity of millennials suggests that since 2011, younger women have been cheating at rates comparable to men. They are also more likely to emulate typically "male" behaviour, focusing on physical arousal, rather than the more typically 'female' desire for emotional connection.
Cheating among the over-60s has also increased since 1991, by at least 10 per cent for women and 14 per cent among men — most likely thanks to longer, healthier lives and drugs that enhance sexual relations at a time when previous generations would have "shut up shop".
There's a basic rule of cheating, which is that the easier it is to do, the more likely we will do it. Many factors — financial independence, physical health, lack of social stigma and so on — are making affairs easier than ever, with fewer consequences if we are caught.
And there's another powerful modern tool for a potential cheater: the internet, which has revolutionised the ease of forming emotional or sexual connections outside of marriage.
Infidelity isn't confined to secret rendezvous in hotels any longer. Today's philanderer can be sharing a meal with their spouse while sending texts to their lover.
Although, over time, many of us lose the intense feeling of being in love with our partner, we rarely lose our desire to be in love and lust again. Without exception, all of my unfaithful patients have used the internet to meet new lovers. And since women tend to be more adept on social media — U.S. research shows 73 per cent use it, compared with 65 per cent of men — it's a path to infidelity with which they are perhaps more likely to feel comfortable.
The internet enables not only instant sexual gratification, but instant intimacy, whether it's chatting to a stranger or rekindling a friendship with a forgotten flame.
For those feeling dissatisfied or simply a bit bored in their current relationship, it's all too easy for an online connection to develop into an emotional affair that activates the powerful desire centres in our brains. Sex may not be on the table — but it's generally under the table and that can create a powerful bond.
In fact, an emotional affair can prove more threatening to a marriage than a sexual affair, due to the way it destroys existing emotional bonds. The chemical rush caused by the affair means you idealise the new lover and turn against your partner — a process psychologists call 'splitting'.
Over my career, I've come to understand that emotional fidelity is the most overlooked aspect of relationship happiness. When an affair is discovered, the emphasis is usually on sexual fidelity, but I think loss of emotional fidelity is more destructive to relationships.
I define it as committing to keep your partner as the central person in your life — your main source of connection and primary confidant. People don't fall in love because they have great sex, they fall in love because of emotional fidelity and their intention to continue it.
And emotional affairs pose the greatest possible threat to this.
Women, in particular, find it hard to accept if their partner has an emotional affair, while men struggle more if infidelity is physical.
But, of course, one can lead to the other. At least one expert says that as many as 80 per cent of emotional affairs will lead to physical encounters.
What drives people to cheat hasn't changed down the generations — it's a combination of biology and opportunity. After all, our brains are programmed by millions of years of evolution to seek sex and love with life-and-death desperation — and it's not just faithful sex in a long-term relationship that we crave.
Genetic diversity is good for the human species, making us taller, healthier and smarter. So our brains have evolved to prompt us to chase new and different sexual partners, instead of the "safe" people we seek out when it comes to marriage.
One study even found that women married to men who shared similar genes related to their immune systems had more affairs.
The truth is that most people live in the grey zone when it comes to fidelity and anyone could fall prey to the temptations modern life is only too keen to provide.
So if you ask the question: "Who is an adulterer?", the answer really should be: "Any one of us."