Rituals that cleanse the body to purify the soul are at the core of religions worldwide. Scientists have now found that these ceremonies apparently have a psychological basis.

Researchers discovered the perception of having committed a sin actually seems to urge people to clean themselves.

They dubbed the phenomenon the "Macbeth effect," after dramatized murderess Lady Macbeth, who vainly tried scrubbing her hands clean of imaginary blood in Shakespeare's famed Scottish play.

Intriguingly, the researchers also found purifying the body helped people absolve their consciences.

"Showering and hand-washing occur daily, but now we find these core routines can really have a psychological impact," behavioral researcher Katie Liljenquist at Northwestern University in Chicago told LiveScience.

Future studies could investigate whether "living in a very clean environment facilitates more ethical behavior, or ironically licenses unethical behavior," Liljenquist added.

Liljenquist and her colleague Chen-Bo Zhong at the University of Toronto first asked undergraduate volunteers to focus on ethical or unethical deeds from their pasts.

The volunteers were more likely to interpret the word fragments "W _ _ H" as "wash" and "S _ _ P" as "soap" if they had been thinking of an unethical deed, and to choose an antiseptic wipe instead of a pencil as free gift.

The investigators also asked each volunteer to hand-copy a short story written in the first person. One group got a story about helping a co-worker; for the other group, the story was about sabotaging a co-worker's efforts.

The participants were then asked to rate various consumer products in what they thought was an unrelated marketing study.

Zhong and Liljenquist found the students who copied the "unethical" story were more likely to rate cleansing products, such as toothpaste and detergent, as more desirable than non-cleansing products, such as batteries and candy bars.

In their last set of experiments, the researchers asked volunteers to first remember an unethical deed they had committed, and then allowed only some of them to wash their hands.

When the students were asked afterward whether they would volunteer, without pay, for another research study to help out a desperate graduate student, 74 percent of those who had not washed their hands offered to help. Only 41 percent of the participants who had had a chance to wash their hands did.

This suggested that volunteers who did not get the chance to clean themselves felt a need "to absolve their consciences," Liljenquist said.

"Past studies have shown there are definite overlaps in the brain in the regions stimulated by moral disgust and physical disgust, the kind you get to potentially bad food or other things you'd evolve to want to avoid," she added.

Whether the psychological impact of cleansing rituals existed before religion adopted them, or arose after religions ingrained cleansing rituals into society, remains an as yet unresolved chicken-or-egg question.

To answer it, Liljenquist said future experiments could explore whether a person's level of religiosity might moderate the "Macbeth effect," and what specific negative emotions trigger it in people.

The researchers reported their findings in the Sept. 8 issue of the journal Science.

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