So you decided to buy a nontoxic cleaning product? Good for you. Just don’t get too self-congratulatory. Purchasing a green product could make you more likely to behave more selfishly down the road, a new study reveals.

Researchers at the University of Toronto asked college students to shop for products online from either an eco-friendly or a conventional store. Then, in a classic experiment known as the dictator game, subjects were asked to divide a small sum of money between themselves and a stranger. Those who shopped at the green store shared, on average, less of their money.

The investigators believe that a “licensing effect” might be at work. “When we engage in a good deed, that gives us a kind of satisfaction,” says Nina Mazar, professor of market­ing and a co-author of the paper. With that self-satisfied feeling can come tacit permission to behave more sel­fishly next time we have the oppor­tunity, Mazar says. Previous research has documented this licensing effect in other contexts; a study published last year revealed that asking people to ruminate on their humanitarian qualities actually reduced their char­itable giving.

Next, Mazar is particularly in­terested in exploring the policy implications of this licensing effect; for instance, one study suggested that people who make their homes more energy-effi­cient start cranking up their heat. She hopes to determine whether simply making people aware of these kinds of tendencies could help combat them.