When Al Gore was caught running up huge energy bills at home at the same time as lecturing on the need to save electricity, it turns out that he was only reverting to "green" type.

According to a study, when people feel they have been morally virtuous by saving the planet through their purchases of organic baby food, for example, it leads to the "licensing [of] selfish and morally questionable behaviour", otherwise known as "moral balancing" or "compensatory ethics".

Do Green Products Make Us Better People is published in the latest edition of the journal Psychological Science. Its authors, Canadian psychologists Nina Mazar and Chen-Bo Zhong, argue that people who wear what they call the "halo of green consumerism" are less likely to be kind to others, and more likely to cheat and steal. "Virtuous acts can license subsequent asocial and unethical behaviours," they write. [See footnote].

The pair found that those in their study who bought green products appeared less willing to share with others a set amount of money than those who bought conventional products. When the green consumers were given the chance to boost their money by cheating on a computer game and then given the opportunity to lie about it – in other words, steal – they did, while the conventional consumers did not. Later, in an honour system in which participants were asked to take money from an envelope to pay themselves their spoils, the greens were six times more likely to steal than the conventionals.

Mazar and Zhong said their study showed that just as exposure to pictures of exclusive restaurants can improve table manners but may not lead to an overall improvement in behaviour, "green products do not necessarily make for better people". They added that one motivation for carrying out the study was that, despite the "stream of research focusing on identifying the 'green consumer'", there was a lack of understanding into "how green consumption fits into people's global sense of responsibility and morality and [how it] affects behaviours outside the consumption domain".

The pair said their findings surprised them, having thought that just as "exposure to the Apple logo increased creativity", according to a recent study, "given that green products are manifestations of high ethical standards and humanitarian considerations, mere exposure" to them would "activate norms of social responsibility and ethical conduct".

Dieter Frey, a social psychologist at the University of Munich, said the findings fitted patterns of human behaviour. "At the moment in which you have proven your credentials in a particular area, you tend to allow yourself to stray elsewhere," he said.

• This footnote was added on 31 March 2010: The study findings above, and the methods used, are challenged by researchers associated with the social psychology department at the London School of Economics, the Institute of Ecological Economy Research in Berlin, and the Institute for Perspective Technological Studies in Seville. Their analysis can be found here: lrcg.co.uk