Shakespeare's Lady Macbeth could never wash away the guilt of murder from her hands, but research has shown that the simple act of hand washing—or even using a wipe—can in fact help people clean their conscience of dirty deeds. A new study, published online May 6 in Science, reveals the power of hand washing to ease people's minds about even mundane decisions.

Often, when people make decisions—no matter how big or small—they tend to justify them, rationalizing often beyond reason that their choice was by far the best.  Resolving the sense of cognitive dissonance vastly decreased in subjects who washed their hands after having to make a simple choice.

In an experiment, 40 subjects had to pick and rank 10 of 30 CDs that they would like to own as if they were completing a consumer survey. They were then given the choice of the fifth- and sixth-ranked CDs. Afterward, as part of an unrelated task, subjects took a survey about liquid soap. Half of the participants were given a soap bottle to assess, and the other half were instructed to try the soap out by washing their hands. Last, the participants were asked to rerank the 10 CDs.

"People who merely examined the soap bottle dealt with their doubts about their decision by changing how they saw their CDs," Norbert Schwarz, of the Department of Psychology at the University of Michigan in Ann Arbor and a co-author on the study, said in a prepared statement. "They saw the chosen CD as much more attractive than before and the rejected CD as much less attractive." Those who had washed their hands, however, appeared to have reduced cognitive dissonance and rated their chosen and rejected CDs about as they had before having to choose between them. 

In a similar experiment, the researchers asked 85 participants to predict how good four different fruit jams would taste and then complete a survey about antiseptic wipes—some people being asked to use them and others only to examine the box. Again, those who had just looked at the wipe boxes later showed typical cognitive dissonance, expecting "the taste of the chosen jam to far exceed the taste of the rejected one," said lead author Spike Lee in a prepared statement. Lee is a graduate researcher in social psychology at the University of Michigan. Those who had used the wipes were more likely to stick to their original ratings.

These findings show that the hand-washing effect is not limited to intense, morally profound situations, but that it "reduces the influence of past behaviors and decisions that have no moral implications whatsoever," Lee noted.

Image courtesy of AAAS/Science