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Emotional infidelity and physical infidelity are often spoken about by marriage experts. But there's a third kind, and it has to do with green things.

There’s an infidelity issue plaguing many modern American marriages, and most spouses don’t even realize it.

It’s called financial infidelity, which is when spouses hide information about their finances from each other. In fact, a study from creditcards.com found that 6 percent of spouses have hidden a bank account from their spouse or partner. And 1 in 5 couples feel it’s OK to spend $500 without telling their partner about it, according to the study.

To find this, researchers interviewed 843 Americans in random telephone interviews and asked about their financial situation with their spouses. They found that hidden bank accounts were a lot more common than they initially thought, according to the study.

There are specific ways spouses will do some “stealth spending,” according to The Wall Street Journal’s blog post on the trend. Spouses will mostly spend in cash, accumulated over a lengthy period of time from different ATM withdrawals, WSJ reported, and they will even hold onto gift cards for the sake of spending them on themselves.

Like the aforementioned study explained, some spouses will also open secret credit card and bank accounts so that they’ll have their own secret cash fund.

These financial cheaters will also deny that they spent any secret money when they’re confronted by their spouse, according to WSJ. In fact, a survey cited by WSJ reported that 64 percent of men will rip up receipts or hide purchases from their spouses to avoid being caught and fighting over money.

“The chances of financial fibbing going on in your home are higher than you think,” WSJ explained. “Whether it wrecks or wrinkles your budget will depend on the gravity of the deception. Although avoiding a fight about money is a positive, doing it by hiding your spending is equally damaging. Addressing the underlying frustrations and challenges that lead to this behavior in an honest way may be painful, but resolving them may be critical.”

Financial battles and concerns have often been noted as one of the leading causes of divorce, especially when they happen early in a relationship, according to The Huffington Post.

In fact, a study from a Kansas State University researcher cited by The Huffington Post found that couples who argued about money in their early days as a couple were more likely to get divorced later in their marriage.

"Arguments about money [are] by far the top predictor of divorce," researcher Sonya Britt told The Huffington Post. "It's not children, sex, in-laws or anything else. It's money — for both men and women."

This isn’t exactly surprising, according to Paula Levy, a marriage therapist in Connecticut, who spoke to creditcards.com. She said most couples keep these financial secrets to avoid conflict with each other.

"In most cases, the secret is mostly to avoid conflict and to make sure they get what they want," Levy told creditcards.com.

Other reasons couples will financially cheat is because one often feels their spouse is a “financial bully,” according to the Deseret News' Lois Collins. In fact, Collins cited a study from Credit Karma that found 1 in 10 spouses considered their married partner to be a financial bully, who controls the money and sets the budgets in an unfair way.

In some cases, one partner will hide expenses from the spouse to avoid conflict over budget issues.

Experts encourage couples to talk openly about their finances so that there aren't any ill feelings shared between partners, Collins reported.

Some experts even recommend partners seek a credit counselor, who can help couples open up about their specific debts, Collins reported. These conversations will open up even more dialogue about how couples can get out of debt, according to Collin’s report.

Regardless of how they do it, experts say spouses need to be open with each other about their finances — even if it gets hard.

“When partners lie or hide money concerns from another, it can have a major impact on their financial future," Ken Lin, chief executive of the counseling service Credit Karma, told Collins. "Many big financial decisions, like applying for a mortgage or saving for a child's education, are made more easily with transparency and communication."

For more on marriage and money:

All aboard: How to win the budget battle with a reluctant spouse

Want to see if your relationship will last? Check your partner's credit score

Does it really matter if you grew up rich and your spouse grew up poor?

Herb Scribner is a writer for Deseret News National. Send him an email at hscribner@deseretdigital.com or follow him on Twitter @herbscribner.