Dubbed the "MacBeth effect", it's the human compulsion to clean up physically after doing wrong morally.
researchers found that study participants who focused on unethical behaviours such as lying, stealing, or betraying friends were more likely to follow up with activities that indicated they felt physically dirty.
Those who were given an opportunity to wash their hands after recalling incidents of immoral behaviour showed signs of a clearer conscious than those who had not washed.
“After we feel morally threatened, we have this deep psychological urge to cleanse ourselves,” says Chen-Bo Zhong at the University of Toronto, Canada, who led the study.
From the New Scientist, Physical washing may help your conscience.