There was a time when farmer’s markets, eco products, recycling, and renewable energy were squarely in the tree hugger’s domain. Then, somewhere along the line, green went mainstream, turning environmental awareness into a socially desirable trait and a mark of the moral man.

But is eco-friendliness really a feather in our cap? When University of Toronto researchers Nina Mazar and Chen-Bo Zhong recently looked into the topic, they found that exposure to green products can under certain circumstances license us to act immorally.

Through a series of experiments, Mazar and Zhong drew the following distinction between two kinds of exposure to green: When it’s a matter of pure priming (i.e., we are reminded of eco products through words or images), our norms of social responsibility get activated and we become more likely to act ethically afterwards. But if we take the next step and actually purchase the green product (thereby aligning our actions with our moral self-image), we give ourselves the go-ahead to then slack off a little and engage in subsequent dishonest behavior.

So in effect, a green purchase licenses us to say “I’ve done my good deed for the day, and now I can focus on my own self-interest.” I gave at the office, I paid my dues, I did my share — that sort of thing. How moral we choose to be at any given moment depends not only on our stable character traits but also on our recent behavioral history.

This implies that if you have two important environmental decisions to make on a given day, your early decision will impact the later one. If for your morning coffee you choose a mug over a paper cup, you may later decide not to recycle. Your cup choice could even affect your subsequent moral choices in other areas, since the moral licensing effect is not domain-specific. (Participants in the above-mentioned experiment, for example, were more likely to cheat and steal cash after making green purchases.)

All this to say that we need to think carefully about the unintended consequences of any early-day decisions we may make ourselves or assign to others.