The Lady Macbeth effect - how physical cleanliness affects moral cleanliness


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"Out, damn spot! Out I say!" In Macbeth's fifth act, Lady Macbeth's role in the treacherous murder of Duncan takes its toll, and she begins obsessively washing her hands to alleviate her guilty conscience. Now, some four centuries after Shakespeare penned his play, scientists have found that physical and moral cleanliness are just as inextricably linked as he suggested.

i-ee9188c27c5d2f17f44668847d94fca1-lmac.jpgThe link between bodily cleanliness and moral purity is evident throughout the world's cultures. Cleansing ceremonies are common in religions. Christians and Sikhs literally wash away their sins through baptism, while the act of wudu sees Muslims prepare for worship by cleaning their bodies. Our language too reveals hints of an overlap - a 'clean conscience' is free of guilt, while 'dirty' is a word for thieves and traitors.

Chen-Bo Zhong from the University of Toronto and Katie Liljenquist from Northwestern University have now revealed the strong links between unblemished hands and stain-free hearts in a series of clever psychological experiments.

They asked two groups of people to remember a good or bad deed from their past. Afterwards, the volunteers solved a simple word puzzle by filling in the missing letters in three incomplete words: W_ _H, SH_ _ER and S_ _P. Remarkably, those who remembered unethical deeds thought of cleaning-related words, like shower, wash and soap, about 60% more often than other words that could equally have fit, like wish, shaker and step. Those who remembered ethical actions showed no such preference.

In another experiment, Zhong and Liljenquist wrongly informed a different group of people that they were taking part in a study investigating links between handwriting and personality. They asked each person to copy a first-person short story, where the protagonist either helped or screwed over a colleague.

Later, the subjects were asked to rate certain household products in terms of desirability. Those who copied selfish stories were much more likely to want cleaning products like Dove soap and Crest toothpaste compared to those who copied selfless tales. Both groups showed equal preferences for random goods like batteries and post-its.

Clearly, memories of moral indiscretions, even if they are not one's own, bring thoughts of cleanliness to the front of the mind. Zhong and Liljenquist believe that physical acts that reduce our levels of physical disgust have a knock-on effect in making us feel morally purer. After all, physical and moral disgust are very similar, with repulsive smells or comments eliciting the same facial reactions and activating overlapping brain regions.

But does it really work? Does cleansing truly absolve our minds of our sins? In a final experiment, the researchers find that, to an extent, it does. People were once again asked to describe a past wrong and some were allowed to wipe their hands with an antiseptic wipe. They were then asked if they would help out another graduate student by helping to pay for a research study. 74% of those who were not offered the wipe agreed. But many of those who wiped their hands also removed their moral stains, and only 41% of them offered help. Physical cleansing effectively halved the chances of future seflessness.

While physical cleanliness clearly goes some way towards restoring moral integrity, it would be foolish to assume that hygiene is a miracle cure for guilt. As Zhong and Liljenquist themselves admit, "There are surely limits to the absolution afforded by a bar of soap."

Reference: Zhong, C. (2006). Washing Away Your Sins: Threatened Morality and Physical Cleansing. Science, 313(5792), 1451-1452. DOI: 10.1126/science.1130726

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Ritual cleansing is folk magic. It only works for people who feel dirty when they've done something wrong. Equating the wrongdoing with filth is of course silly, just the silly kind of thing grownups inflict on little kids when they're yelling at them in a rage.

This sounds very plausible, but I have an issue with the methodology for the first study. The published data uses the average number of cleansing related words chosen for each group - but if they were only doing these three words, then I would strongly expect someone who chose one cleansing word to also choose others through word association.

Given that the sample size is only 30 per group, I think the significance may have been overestimated, and the average was the wrong measure to use in this case. Had they been doing a longer list of words, I would be less sceptical, or if they had grouped people into those who chose some cleansing words and those who chose none.

By Charlotte (not verified) on 05 Jul 2008 #permalink

This is something I'm sceptical about in a certain way. Whilst undoubtedly there is a clear link there, how can we tell that it is not culturally ingrained, rather than being hard-wired into human brains? I would make the claim that the social sciences (I know, ewwww to any hard, physical scientist) have a larger part to play in shaping the picture of this. Anthropologists have a long history of trying to deal with this problem, in particular the work of Mary Douglas, and anyone who has attempted to look at ritual or religion. The methodology of the psychological studies is not something I feel has any large flaws as suggested by Charlotte. I simply feel that the verification/falsification can only be done by studying other cultural attitudes and finding out if it is truly universal.