Hand washing removes more than dirt—it also removes the guilt of past misdeeds, weakens the urge to engage in compensatory behavior, and attenuates the impact of disgust on moral judgment. These findings are usually conceptualized in terms of a purity-morality metaphor that links physical and moral cleanliness; however, they may also reflect that washing more generally removes traces of the past by metaphorically wiping the slate clean. If so, washing one’s hands may lessen the influence of past behaviors that have no moral implications at all. We test this possibility in a choice situation. Freely choosing between two similarly attractive options (e.g., Paris or Rome for vacation) arouses cognitive dissonance, an aversive psychological state resulting from conflicting cognitions. People reduce dissonance by perceiving the chosen alternative as more attractive and the rejected alternative as less attractive after choice, thereby justifying their decision.The authors tested whether hand washing reduces this classic postdecisional dissonance effect (the need to justify a recent choice) by designing a ranking and choice experiment in which participants, after making a choice, were subsequently asked to evaluate a soap - some with actual hand washing and some without. Their finding:
...indicate that the psychological impact of physical cleansing extends beyond the moral domain. Much as washing can cleanse us from traces of past immoral behavior, it can also cleanse us from traces of past decisions, reducing the need to justify them. This observation is not captured by the purity-morality metaphor and highlights the need for a better understanding of the processes that mediate the psychological impact of physical cleansing. To further constrain the range of plausible candidate explanations, future research may test whether the observed "clean slate" effect is limited to past acts that may threaten one’s self-view (e.g., moral transgressions and potentially poor choices) or also extends to past behaviors with positive implications.