Xu, A., R. Zwick, and Norbert Schwarz. 2012. "Washing Away Your (Good or Bad) Luck: Physical Cleansing Affects Risk-Taking Behavior." Journal of Experimental Psychology-General, 141(1): 26-30.
Many superstitious practices entail the belief that good or bad luck can be "washed away." Consistent with this belief, participants who recalled (Experiment 1) or experienced (Experiment 2) an episode of bad luck were more willing to take risk after having as opposed to not having washed their hands, whereas participants who recalled or experienced an episode of good luck were less willing to take risk after having as opposed to not having washed their hands. Thus, the psychological effects of physical cleansings extend beyond the domain of moral judgment and are independent of people's motivation: incidental washing not only removes undesirable traces of the past (such as bad luck) but also desirable ones (such as good luck), which people would rather preserve.