photoWhen you suffer a hit to your ego, it might be a good idea to postpone any shopping trips. A new psychology study suggests people are more likely to use their credit cards when their self-esteem is low.

Why credit cards and not cash? Researchers Niro Sivanathan of the London Business School and Nathan Pettit of Cornell University say actually parting with cash can be psychologically painful

The researchers had people work on an ambiguous computer test, and then told half of them that their "spatial reasoning and logic ability was in the 12th percentile," which is a scientific-sounding way of telling them they're not very smart.

They told the other half that they were in the 88th percentile, a perfectly fine performance.

When asked how they might pay for "a consumer product that you have been considering purchasing," people who'd had their ego threatened were substantially more likely to say they were planning on paying on credit.

In a follow-up study, Sivanathan and Pettit asked 150 college students to think about buying a pair of jeans. Half were told to consider a pair of exclusive, high status designer jeans, while the rest were told to think about normal, everyday jeans. The students then went through the same computer test, and were told they had done poorly or well.

The self-esteem threat made people willing to pay almost 30 percent more for the luxury jeans, and were more than 60 percent more likely to intend to purchase the jeans with a credit card.

Does threat make any purchase look good, or are luxury items particularly good at repairing self-esteem? The students who thought about everyday jeans did not increase how much they would pay for regular jeans when threatened, and the threat did not change their willingness to use credit over cash.

Luxury items are especially effective at reassuring us of our value, the researchers say.

The lesson for consumers is, when you're feeling blue, stay away from the mall.