Confident with my choice (Image: Gagilas Photo/Flickr/Getty)

Long a metaphor for the desire to distance oneself from immoral acts, hand washing doesn’t just wipe the conscience clean – it also changes how an individual regards a decision they have just made.

Lady Macbeth notwithstanding, the physical act of washing one’s hands is known to ease the guilt we feel about past unethical deeds. Now it seems that the act also removes our natural inclination to validate even trivial past decisions.

It is known that after people have made a decision – be it a big one such as choosing which politician to vote for or a trivial one such as which CD to buy – they tend to exaggerate its benefits. They also overplay the potential downsides of options they rejected.


“People focus on the positive features of their choice and the negative features of the rejected option,” says Spike Lee at the University of Michigan, Ann Arbor. “As a consequence, they come to like the choice they made better.”

Soap test

To see whether hand-washing affects this justification process, Lee first asked 40 students to rank 10 CDs by how much they liked them. He then asked them to choose between owning either their fifth or sixth-ranked CD.

Next he asked half the volunteers to evaluate the quality of a liquid soap by washing their hands and the other half to examine the soap by observation only. Then, all students ranked the original 10 CDs again.

Lee’s team found that, in the second CD ranking, those who had not washed their hands increased the ranking of the CD they had chosen to keep – which had originally been either their fifth or sixth choice – by two places compared with its original ranking, and pushed the rejected CD down by two places, on average.

This was a sign that they were justifying their choice of which CD to keep, says Lee; the expected pattern of behaviour.

But for those who washed their hands before ranking the CDs for a second time, the order tended not to change. In other words, their choice of which CD to keep did not change the way that they went on to rank that CD, when given a second chance to do so.

Washing away enjoyment

When the researchers repeated the same experiment using choices of jam instead of CDs, and antiseptic wipes instead of soap, the results were the same. They conclude that the hand washing removes the usual tendency to justify a decision that has already been made.

On one hand, Lee says, this is a more rational way of thinking. But there’s also a catch. “Justification has a purpose, it makes people feel good. Washing away the need to justify past decisions also washes away the cognitive good.” It’s possible that those who washed their hands won’t enjoy the CD or jam as much as their unwashed counterparts will, he says.

Katie Liljenquist of Brigham Young University in Provo, Utah, who first demonstrated that hand-washing changes psychological behaviour, calls this “exciting work”.

It shows that daily tasks can have profound effects on our psychology in more ways than we knew, she says. “And it’s fun to see how metaphors in daily life, such as wiping the slate clean, can typify human behaviour.”

Journal reference: Science, DOI: 10.1126/science.1186799