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Washing hands with soap.

Photograph by Mark Thiessen, National Geographic

Rachel Kaufman

for National Geographic News

Published May 6, 2010

If you're trying to clear your head after making a tough choice, you should wash your hands, new research suggests.

Aside from hygiene, the simple act of hand washing seems to "wipe away" the traces of decisions that leave a person feeling conflicted, said study co-author Spike W. S. Lee, a doctoral student in psychology at the University of Michigan.

After making hard choices, people tend to justify their decisions to make themselves feel better, Lee explained. (Related: "Brain Region for Overcoming Fear, Anxiety Found.")

"You want to feel that you made the right choice, so you justify it by thinking about the positive features" of your decision, he said. This process is called postdecisional dissonance.

But when people in the study washed their hands after making such a choice, they no longer felt a subconscious need to rationalize.

"Our physical experience actually influences our mental experience," Lee said. (Video: the science of stress.)

Wiping the Slate Clean

To test the effects of washing, Lee and co-author Norbert Schwarz asked student volunteers to participate in what they thought was a consumer survey.

One group of 40 students was asked to rank ten music CDs in order of preference. The students were then offered a gift: Take home either your fifth- or sixth-ranked CD.

Once they'd made a decision, some students opted to evaluate a liquid hand soap by washing their hands, while others just looked at the bottle.

The students who didn't wash their hands later ranked their chosen CDs higher than they had before—a classic example of postdecisional dissonance.

But students who did wash up ranked the ten CDs in basically the same order as before.

The researchers conducted a similar survey in which they asked 85 people to chose a jam without tasting it first. People who didn't use an antiseptic wipe expected their chosen jam to taste better than the rejected one.

Those who used the wipe thought the jams would taste about the same.

It's as if hand-washing in any form "wipes the slate clean" and removes the residual feelings and rationalizations associated with the choice, Lee said.

(Related: "'Undecided' Voters' Minds Already Made Up, Study Says.")

Psychology of Dirty Socks

Next, the researcher wants to look into whether this psychological phenomenon extends into other areas of cleanliness.

"There are these baseball players who have lucky socks that they don't wash. Why is that?" Lee asked.

"Maybe there's the belief that there's positive particles of luck that you don't want to remove."

The hand-washing research will be published in this week's issue of the journal Science.

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