FOR A CLEAN CONSCIENCE

And it works, at least for minor guilt stains. People who washed their hands after contemplating an unethical act were less troubled by their thoughts than those who did not, the study found.

8220;The association between moral and physical purity has been taken for granted for so long that it was startling that no one had ever shown empirical evidence of it,8221; said Chen-Bo Zhong, an author of the new research and a behavioural researcher at the University of Toronto. The study, which he wrote with Katie Liljenquist, a graduate student at Northwestern University, appeared in the journal Science.

The researchers call this urge to clean up the 8220;Macbeth effect,8221; after the scene in Shakespeare8217;s tragedy in which Lady Macbeth moans, 8220;Out, damned spot! Out, I say!8221; after bloodying her hands when her husband, at her urging, murders his master, King Duncan.

In one of several experiments among Northwestern undergraduates, the researchers had one group of students recall an unethical act from their past, like betraying a friend, and another group reflect on an ethical deed, like returning lost money. Afterward, the students had their choice of a gift, either a pencil or an antiseptic wipe. Those who had reflected on a shameful act were twice as likely to take the wipe.

In another experiment, the researchers found that students who had been contemplating an unethical deed rated the value of cleaning products significantly higher than peers who had been thinking about an ethical act.

Psychologists have known for years that when people betray their values, they feel a need to compensate. Christians who read a blasphemous story about Jesus express a desire to go to church more frequently; social liberals who feel they discriminated express an increased desire to volunteer for civil rights work.

8220;It8217;s sometimes called symbolic cleansing, or moral cleansing, and it8217;s an attempt to repair moral identity,8221; said Dr Philip Tetlock, a professor of organisational behaviour at the University of California, Berkeley. Sure enough, Zhong and Liljenquist found that students who had been thinking about past sins were very likely to agree to volunteer their time to help with a graduate school project8212;unless they had been allowed to wash their hands, which cut their willingness to volunteer roughly in half.

Several people known to have expressed guilt over spreading rumours were asked to comment for the record on the findings, but all declined. And efforts to contact hit men to inquire about personal hygiene were deemed unwise; none had publicists.

Liev Schreiber, who played Macbeth to critical acclaim this summer in Central Park, said the moral weight of the murder in the play was exhausting. And he said cast members lined up to shower at the theatre, rather than waiting until they got home. 8220;That was unusual8212;usually no one uses those theater showers,8221; Schreiber said.

The murder of a king, Zhong acknowledged, falls into a different category from the confessed sins of the undergraduates, which included shoplifting, lying and 8220;kissing a married man.8221;

8220;We do believe there might be limits to how well simple hand washing can clean your slate,8221; he said, 8220;but it remains to be seen where that limit is.8221;

BENEDICT CAREY