The smell of citrus promotes generosity, while dim rooms increase dishonesty and selfish behaviour, psychology researchers suggest in recent studies.

Chen-Bo Zhong, a psychologist at the University of Toronto, and his colleagues in the U.S. have conducted a series of small experiments designed to test how changes in an environment -- differences in lighting or smell -- can affect human behaviour.

Zhong said that the rooms with the dim lighting created a sense of anonymity, what he calls illusory anonymity.

"The idea is that when we experience darkness, we disregard what other people may still be able to see or hear or observe," he said. "The illusory sense of anonymity can license unethical behaviour."

In previous research, Zhong and his colleagues explored the connection between unethical behaviour and physical cleanliness, something Zhong called the Lady Macbeth effect, after the Shakespeare character who obsessively washed her hands because of her role in the murder of the king ("Out, damn spot. Out, I say!").

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