There are many health reasons to wash your hands, but it can also have psychological effects. Specifically, it may lessen guilty feelings or remorse over past actions—or at least serve as an attempt to do so. Many religions and poets have linked physical and spiritual cleansing, of course. And metaphors abound about “washing your hands” of something disagreeable.
During the last decade researchers, using a variety of psychological tests, have found that handwashing can indeed have a psychologically cleansing effect. In one study, for instance, people asked to recall unethical deeds from their past were more likely to feel a need to clean their hands, and felt somewhat less regretful after doing so. A few years ago, in a study in Science, college students who washed their hands (or used hand wipes) felt less remorse and did less second-guessing after choosing between two good options.
Handwashing is unlikely to alleviate remorse over extreme misdeeds—witness guilt-ridden Lady Macbeth, who feverishly scoured an imagined bloodstain on her hands (“Out, damned spot!”) to no avail. But next time you feel guilty over, say, eating too many cookies or yelling at your spouse, besides resolving to do better next time, see if a good scrub helps.