How hand-washing helps ease your mind

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The simple act of hand-washing has been shown to help clear a guilty conscience and even make you more forgiving of the moral missteps of others. It’s known as the Macbeth principle of morality: we make a fundamental, psychological association between physical purity and moral purity, which lets us literally wash away our sins (and explains why bathing is central to so many religious rituals).

The trick even works in the opposite direction, with cleanliness prompting moral behavior: in one study, people exposed to a clean-smelling environment were induced to act more fairly and charitably toward strangers than people in a neutral-smelling place.

Now a new study published Friday in Science asks whether hand-washing can wipe the slate clean of any past behavior — even everyday decisions, like, say, choosing Paris over Rome for vacation.

When people make choices, especially between two similarly attractive options, they tend to go to great lengths to justify them — exaggerating Paris’s charms over Rome’s — as psychological assurance they’ve made the right decision.

The mental exercise reduces post-decisional dissonance — that lingering bad feeling that you’re missing out on the cast-off option — and the authors of the new study found that hand-washing eliminated people’s need to do it. Here’s how the experiment went, according to the paper:

As part of an alleged consumer survey, 40 undergraduates browsed 30 CD covers as if they were in a music store. They selected 10 CDs they would like to own and ranked them by preference. Later, the experimenter offered them a choice between their fifth- and sixth-ranked CDs as a token of appreciation from the sponsor. After the choice, participants completed an ostensibly unrelated product survey that asked for evaluations of a liquid soap; half merely examined the bottle before answering, whereas others tested the soap by washing their hands. After a filler task, participants ranked the 10 CDs again.

“People who merely examined the soap bottle dealt with their doubts about their decision by changing how they saw the CDs: as in hundreds of earlier studies, once they had made a choice, they saw the chosen CD as much more attractive than before, and the rejected CD as much less attractive,” said study co-author Norbert Schwarz, a psychologist at University of Michigan, in a statement. “But hand-washing eliminated this classic effect. Once participants had washed their hands, they no longer needed to justify their choice when they ranked the CDs the second time around.”

The researchers repeated the experiment, this time asking participants to rank the desirability of four kinds of fruit jam. Once again, volunteers who cleaned their hands with an antiseptic wipe after choosing, showed the kind of satisfaction with their decision that the non-wipers lacked. “Much as washing can cleanse us from traces of past immoral behavior, it can also cleanse us from traces of past decision, reducing the need to justify them,” the authors write.

Still, there’s no guarantee that a bout of hand-washing will stave off post-decision remorse in the long run — though it will probably help keep you from catching a cold. As far as those big decisions go, however, you’re probably best off engaging in good old-fashioned justification.