Millennials don’t shop like their parents—and increasingly, they don’t pay like their parents either. Studies have already shown that many of them have chucked the checkbook (if they’ve ever had one); and they’re more likely to forego cash as well, a poll released today by CreditCards.com found. Asked how they typically pay for purchases under $5, 77% of people over 50 surveyed preferred cash to debit or credit, while just 48% of people between 18 and 29 use paper money. The fact that millennials are using cards to pay for even such small expenses suggests they’re probably using plastic for most purchases. And when they’re swiping, this group also uses debit (37%) vs. credit (14%) by a larger margin than any other cardholder group. What millennials may not realize is that choosing plastic—even if it’s debit—over paper could be costing them. Research has suggested that we’re inclined to spend more when we swipe. A 2008 study published in the Journal of Experimental Psychology found that physically handing over bills triggers an emotional pain that actually helps to deter spending, while swiping doesn’t create the same aversion. As a result, the study found, cash discourages spending whereas plastic encourages it. In addition, a 2012 study from The Journal of Consumer Research found that shoppers who pay with plastic focus more on the benefits of the purchase than the price, while those who pay with cash focus on price first. In other words, we’re more likely to make the decision to purchase an item when we know we’ll be charging it. Further fueling our natural tendencies to spend more with plastic—a.k.a. “the credit card premium”—is the fact that many shops and bars mandate that you spend a minimum amount to use your card. So if you were planning to use the card anyway, you might pad your purchase to get to the minimum required. All this spending on plastic also can cause you to rack up debt or overdraft fees, if you’re not swiping mindfully. And many members of Gen Y are not, it would seem. For example, millennials are more likely than any other age group to overdraw their checking accounts, the Consumer Financial Protection Bureau found. About 11% of millennials overdraft more than 10 times a year, and these overdrafts were typically for small purchases under $24 and were paid back within three days. With the median overdraft fee equaling $34, borrowing $24 for three days is like taking out a loan with a 17,000% annual percentage rate, the study found. Of course, we can avoid paying the credit card premium by just using cash. But if you won’t remember to go to the ATM, at least take a second to close your eyes the next time you’re about to buy something using plastic: Think about the price of the item and how it will impact your bank account. You might even give yourself a 24-hour cooling off period to think over any nonessential purchases. Avoid overdrawing or getting in over your head in debt by reviewing your bank and/or credit card account online once per day, or by using an app like Mint.com, which lets you track all your accounts in one place. Also, consider setting alerts at your bank or credit card website to let you know when you’re approaching a certain balance—this can keep your spending in check. Related: Money 101: How Do I Figure Out My Financial Priorities? Money 101: How Do I Create a Budget I Can Stick To?