Cleaning one's hands does not only remove dirt, scientists have also found evidence that it removes residues of the past - like the feeling of guilt or doubts about past decisions. This is called the clean-slate effect.
Physical and moral cleanliness
- “clean hands and a pure heart” vs. ”dirty hands” or “dirty mouth”-
People response to moral transgression with disgust, an emotion associated with e.g. spoiled food. They express similar facial expressions, activation of overlapping neural networks and comparable subjective feelings.
The reuse model of embodied cognition explains this phenomena through evolution. Complex higher cognitive functions most likely built up on existing mechanisms. The parallel between physical and moral disgust therefore may have giving rise to the conceptual metaphor that links physical and moral purity with cleanliness. Various experiments support this hypotheses.
For example participants of an experiment had to judge the severity of others' moral transgressions while sitting in a dirty smelly room vs. in a clean room. The group surrounded by a dirty environment expressed stronger moral condemnation than the once in the clean room.
Therefore physical dirtiness influences perceivers’ moral evaluation.
This relationship has motivational and behavioural consequences. If remembering one’s own moral transgressions also leaves one with a dirty feeling, it should therefore elicit the desire to cleanse. An experiment conducted by Lee and Schwarz asked people to convey a lie by voice mail (using their mouth) and email (hand), followed by an evaluate of several consumer products, including mouthwash and hand sanitiser.
Participants who had been lying with their mouth preferred mouthwash over and sanitisers where as people who lied with their “hands” preferred hand sanitiser. Moreover, participants were also willing to pay more for the product that cleansed their “dirty” body part. These findings suggest a parallel between physical and moral contamination.
Consequences of cleaning
Other studies found proof that physical cleansing restore moral cleanliness. Cleansing most likely attenuate disgust and therefore results in less condemnation, less guilt and less compensatory helping behaviour. Furthermore if a person feels very “clean” when witnessing an immoral act, the physical cleanliness translate into a sense of moral superiority that renders others immoral act.
The psychological impact of cleanliness/dirtiness is therefore context sensitive.
https://www.researchgate.net/publication/254081738_Wiping_the_Slate_Clean_Psychological_Consequences_of_Physical_Cleansing