Clean hands, clean minds: The psychological impact of physical cleanliness

This past Saturday, October 15th, marked a momentous occasion in the history of cleanliness: the fourth annual Global Handwashing Day. Yes, it exists. Established by the Global Public Private Partnership for Handwashing with Soap in 2008, it has since been celebrated by schools, families, and villages across the world, from China, to Peru, to Burkina Faso. And it's not just a gimmick: proper handwashing has the potential to save more lives than any vaccine or medical intervention and is one of the simplest and most cost-effective ways of preventing disease. But what's more, it's also an incredibly powerful psychological tool.


We tend to consider moral transgressions in terms of physical cleanliness

Consider this recent review from Current Directions in Psychological Science, which explores the consequences that hand washing has on the mind. The series of studies that the authors explore take as their starting point the historically close association between physical disgust and moral disgust: when we perceive a moral transgression, we tend to react in a similar way as we would to something that is physically off-putting, such as spoiled food or physical contaminants in the environment. We recoil in the same fashion; our face scrunches up in the same repulsed expression; even our brain lights up in overlapping neural networks, evoking similar subjective feelings in both instances.

And when we think about morality, we tend to think about it in terms of physical cleanliness. In one demonstration of this effect, researchers asked people to think abut a past behavior that was either moral or immoral. Those who thought about immoral acts were later far more likely to fill in word fragments such as W _ _ H and S _ _ P with words related to cleanliness, such as wash and soap, whereas no such effect was observed in any other group. On the flip side, people who were exposed to either a messy room, a stinky smell (including a “fart spray" in one study), or a video that showed a dirty toilet were more likely to judge others' moral transgressions as more severe and more deserving of punishment than people who made the same judgments while sitting in a clean room.

Physical cleaning has psychological consequences

Moreover, in both cases, the effect did not stop with the mind: the “dirty" feeling of moral transgression also activated the desire to cleanse oneself physically. The same researchers who asked people to think of moral or immoral acts later had them choose a parting gift: a pencil or an antiseptic wipe. Those who had thought of immoral actions were much more likely to choose the wipe.

And, the effect is body-part specific: if you speak a lie, you are more likely to want to clean your mouth; if you email that same lie, you are more likely to want to clean your hands. Not just more likely — you will actually pay more for the proper cleaning implement (i.e., mouthwash, hand sanitizer) to accomplish your desired goal.

Lady Macbeth was making an important point when she tried so diligently to scrub away that damned spot from her white hands. But, while for her, the process proved futile—her transgression was much too severe for the simple remedy—for others, it could have important psychological consequences. In one study, participants were asked to recall a personal immoral experience from their past. Some were then given a hygienic wipe, ostensibly as part of a protocol for using public computers, while others received nothing. Those who received nothing were later much more likely to volunteer for another project, while those who had wiped their hands were less inclined to do so, suggesting that their guilt had already been lessened by the physical act of hand cleaning. And, in a parallel study to that described earlier, of judging others' moral transgressions after watching a disgusting movie, the effect of judging others more harshly disappeared if participants washed their hands before making the judgment.

Washing your hands is important for more than your physical health

So, being clean has an important psychological impact not just on our judgment of ourselves, but on our perception of others. It's a short step between physically dirty and psychologically so. And conversely, keeping clean can mean good things for our psychological wellbeing as well as our judgment of others' actions and moral states.

We've long known that handwashing is important for the health of the body. But it is also a central tool in the maintenance of the mind. So think about that, next time you lather up (for at least 20 seconds, of course, with hot water and plenty of soap—otherwise, you've learned nothing from the Global Handwashing initiative).

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New fossils suggest human ancestors evolved in Europe, not Africa

Experts argue the jaws of an ancient European ape reveal a key human ancestor.

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  • The jaw bones of an 8-million-year-old ape were discovered at Nikiti, Greece, in the '90s.
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Homo sapiens have been on earth for 200,000 years — give or take a few ten-thousand-year stretches. Much of that time is shrouded in the fog of prehistory. What we do know has been pieced together by deciphering the fossil record through the principles of evolutionary theory. Yet new discoveries contain the potential to refashion that knowledge and lead scientists to new, previously unconsidered conclusions.

A set of 8-million-year-old teeth may have done just that. Researchers recently inspected the upper and lower jaw of an ancient European ape. Their conclusions suggest that humanity's forebearers may have arisen in Europe before migrating to Africa, potentially upending a scientific consensus that has stood since Darwin's day.

Rethinking humanity's origin story

The frontispiece of Thomas Huxley's Evidence as to Man's Place in Nature (1863) sketched by natural history artist Benjamin Waterhouse Hawkins. (Photo: Wikimedia Commons)

As reported in New Scientist, the 8- to 9-million-year-old hominin jaw bones were found at Nikiti, northern Greece, in the '90s. Scientists originally pegged the chompers as belonging to a member of Ouranopithecus, an genus of extinct Eurasian ape.

David Begun, an anthropologist at the University of Toronto, and his team recently reexamined the jaw bones. They argue that the original identification was incorrect. Based on the fossil's hominin-like canines and premolar roots, they identify that the ape belongs to a previously unknown proto-hominin.

The researchers hypothesize that these proto-hominins were the evolutionary ancestors of another European great ape Graecopithecus, which the same team tentatively identified as an early hominin in 2017. Graecopithecus lived in south-east Europe 7.2 million years ago. If the premise is correct, these hominins would have migrated to Africa 7 million years ago, after undergoing much of their evolutionary development in Europe.

Begun points out that south-east Europe was once occupied by the ancestors of animals like the giraffe and rhino, too. "It's widely agreed that this was the found fauna of most of what we see in Africa today," he told New Scientists. "If the antelopes and giraffes could get into Africa 7 million years ago, why not the apes?"

He recently outlined this idea at a conference of the American Association of Physical Anthropologists.

It's worth noting that Begun has made similar hypotheses before. Writing for the Journal of Human Evolution in 2002, Begun and Elmar Heizmann of the Natural history Museum of Stuttgart discussed a great ape fossil found in Germany that they argued could be the ancestor (broadly speaking) of all living great apes and humans.

"Found in Germany 20 years ago, this specimen is about 16.5 million years old, some 1.5 million years older than similar species from East Africa," Begun said in a statement then. "It suggests that the great ape and human lineage first appeared in Eurasia and not Africa."

Migrating out of Africa

In the Descent of Man, Charles Darwin proposed that hominins descended out of Africa. Considering the relatively few fossils available at the time, it is a testament to Darwin's astuteness that his hypothesis remains the leading theory.

Since Darwin's time, we have unearthed many more fossils and discovered new evidence in genetics. As such, our African-origin story has undergone many updates and revisions since 1871. Today, it has splintered into two theories: the "out of Africa" theory and the "multi-regional" theory.

The out of Africa theory suggests that the cradle of all humanity was Africa. Homo sapiens evolved exclusively and recently on that continent. At some point in prehistory, our ancestors migrated from Africa to Eurasia and replaced other subspecies of the genus Homo, such as Neanderthals. This is the dominant theory among scientists, and current evidence seems to support it best — though, say that in some circles and be prepared for a late-night debate that goes well past last call.

The multi-regional theory suggests that humans evolved in parallel across various regions. According to this model, the hominins Homo erectus left Africa to settle across Eurasia and (maybe) Australia. These disparate populations eventually evolved into modern humans thanks to a helping dollop of gene flow.

Of course, there are the broad strokes of very nuanced models, and we're leaving a lot of discussion out. There is, for example, a debate as to whether African Homo erectus fossils should be considered alongside Asian ones or should be labeled as a different subspecies, Homo ergaster.

Proponents of the out-of-Africa model aren't sure whether non-African humans descended from a single migration out of Africa or at least two major waves of migration followed by a lot of interbreeding.

Did we head east or south of Eden?

Not all anthropologists agree with Begun and his team's conclusions. As noted by New Scientist, it is possible that the Nikiti ape is not related to hominins at all. It may have evolved similar features independently, developing teeth to eat similar foods or chew in a similar manner as early hominins.

Ultimately, Nikiti ape alone doesn't offer enough evidence to upend the out of Africa model, which is supported by a more robust fossil record and DNA evidence. But additional evidence may be uncovered to lend further credence to Begun's hypothesis or lead us to yet unconsidered ideas about humanity's evolution.