In a study reported in tomorrow's issue of Science, Spike W. S. Lee and Norbert Schwarz of the University of Michigan asked subjects to rank the top 10 CDs they'd like to own from a list of 30, then choose to keep either their fifth- or sixth-ranked disc. (This presumably was a tough call.) Subjects then evaluated some hand soap, half by looking at the bottle and half by actually using it. Finally they ranked their top 10 CDs again.

Subjects who didn't use the soap now ranked their chosen CD about two places higher than the one they didn't pick. Increasingly valuing a chosen option and devaluing the unchosen one is a typical effect of cognitive dissonance. But for those who washed their hands, relative rankings of the two CDs remained about the same. The angst was erased.

Lee and Schwartz repeated the demonstration by asking another set of subjects to choose between two jars of jam. Then subjects evaluated antiseptics wipes by using them or looking at them. Finally subjects rated how good they thought the jams would taste. The wipers expected equal tastiness, while the others expected significantly more scrumptiousness from their preferred jar.

Previous research linking disgust and moral purity has shown that recalling an unethical act increases the desire to atone and that this increase is attenuated by hand-washing. Lee and Schwartz suggest that that Lady Macbeth effect and their own results might both be subcases of a broader "clean slate effect": washing may expunge the emotional power of past acts--perhaps even good ones--from the mental record.

Of course there's probably a reason we evolved to reduce cognitive dissonance by revaluing our options post-decision--perhaps to eliminate buyer's remorse. Surely a happy romantic partnership would be tough if you're always thinking "maybe I should have picked the blonde." So you might not want to mess with such a system. But it looks like second-guessing every little thing is the price you have to pay for good hygiene.