“My 2019 resolution is to say things on air that I say off air…” – the famous last words of Pete Hegseth last year, just before he revealed a secret that set the internet alight.

At the time, Hegseth was best known as a presenter who had a sprinkling of controversial views. Then he said: “I don’t think I’ve washed my hands for 10 years.” Cue a collective wrinkling of noses, and a frenzy of articles about what might be on your hands after a decade.

Disconcertingly, Hegseth is in good company; in 2015 the actress Jennifer Lawrence dropped the bombshell that she almost never washes her hands after going to the bathroom. (They both later said they had been joking). That same year, the Republican Senator for North Carolina suggested that requiring restaurant employees to wash their hands was a classic example of over-regulation.

While 10 years is hopefully some kind of record, observant bathroom-users everywhere will already have noticed that non-hand-washers are alarmingly widespread. One study estimated that in 2015, just 26.2% of global bathroom visits with potential “faecal contact” were followed by hand washing with soap.

“It sounds like such a simple behaviour,” says Robert Aunger, an expert in evolutionary public health at the London School of Hygiene and Tropical Medicine. “But, you know, we’ve been working on it [getting people to wash their hands more] for 25 years and it’s still very low.”

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Of course, this can partly be explained by the lack of adequate facilities and soap in poorer parts of the world. In the least developed countries, only 27% of the population has access to these things (The World Health Organization and UNICEF estimate that around three billion people don’t have either at home). But even in many high-income nations, where both are abundant, only 50% of people actually use them after going to the toilet – surely enough for us to consider making ankle greetings permanent.

These statistics are particularly jarring, when you consider that washing your hands is thought to be one of the most life-saving inventions in the history of humankind – contributing to an average lifespan which now hovers around 80 years in countries like the UK, rather than 40 or so as was the case in 1850, when hand washing was first popularised.

As if we needed any further incentives, this simple hygiene habit also provides the attractive possibility of eluding superbugs and pandemics. A 2006 review found that regularly washing your hands can cut your risk of respiratory infections by between 6 and 44%. Since the Covid-19 pandemic emerged, scientists have found that a country’s handwashing culture is a “very good” predictor of the degree of its spread.

(The virus is mostly thought to infect people through particles suspended in the air, but it can also enter the body after a person touches contaminated objects and then their face. (Read more about why we can’t stop touching our faces.))

Why are some of us such enthusiastic hand-cleaners that we will pay £360 for hand sanitiser during a shortage, while others stubbornly refuse to simply pick up the soap? And if mysterious new viruses and horror stories about faeces on hotel TV remotes can’t coax people into changing their habits, what will?

It turns out that failing to stop by the sink on your way out of the bathroom might not just be down to laziness. From a person’s style of thinking to their degree of delusional optimism, the need to feel “normal” and the potency of their feelings of disgust, a number of psychological factors are subliminally discouraging people from washing their hands. By understanding these hidden biases, experts around the world are hoping they can lure us into becoming more hygienic.

“One problem with handwashing is that, especially in developed countries, you can avoid washing your hands lots and lots of times and you won’t get ill,” says Aunger. When it does make you ill, it’s often days later, by which point that time you forgot will have long vanished from your memory. “Even with coronavirus, they’re saying the delay between being infected and seeing any symptoms is like five, six days, so the connection is very difficult to make.”

Beware of optimism

One factor that’s thought to have an impact is optimism. The “optimism bias” involves believing that bad things are less likely to happen to ourselves than they are to other people. This irrationally positive outlook is universal – found in diverse human cultures and across demographics such as gender and age, and even in some animals, such as starlings and rats. It leads us to miscalculate our chances of a range of unpleasant events, from developing cancer to getting divorced.

This delusion may be partly responsible for things like smoking, or why many people choose credit cards that end up costing them money. It may also stop some people from washing their hands. One study, which was conducted at a large university in New York amid the 2009 swine flu (H1N1) pandemic, found that students who had higher levels of unrealistic optimism were less likely to intend to wash their hands. Meanwhile, those who had a greater confidence in their ability to control their own lives were the opposite.

The optimism bias has also been found in student nurses, who tend to overestimate their knowledge of good hand-hygiene practices, and people who handle food for their jobs, who consistently underestimate their risk of causing food poisoning in others.

Social norms matter

A big clue to the importance of psychology in hand washing lies in the extraordinary range of hand hygiene practices in different cultures around the world. For one French study, 64,002 people across 63 countries were asked if they agreed with the statement “washing your hands with soap after using a toilet is something you do automatically”. Less than half the respondents from China, Japan, South Korea and the Netherlands agreed. Meanwhile, the country with hands-down (sorry) the best rates was Saudi Arabia, where 97% of people said they habitually washed their hands with soap.

Even within countries, we’re not all equally guilty of crimes against hygiene.

For example, studies have consistently shown that women are considerably more diligent at handwashing than men; in one of his own studies, Aunger found that women were twice as likely to wash their hands at motorway service station toilets in the UK. The trend has even extended into the Covid-19 pandemic, with one recent poll finding that 65% of women and 52% of men say they are washing their hands regularly.

Aunger explains that the variation in hand washing is probably down to social norms – a powerful set of informal rules that govern our behaviour when we’re in a group. “They’re complex psychological systems, which depend on seeing what other people do, thinking what other people expect you to do, and experiencing pressure to copy it,” he says.

If we see others washing their hands in the bathroom, that’s what we do – but crucially, when nobody’s doing it, there’s a pressure not to either. “And in fact, people can be seen as being unusual or ‘above themselves’ if they do,” says Aunger. Indeed, a 2018 study found that how much a person thought other people were washing their hands was significantly linked to how often they said they washed their own.

Since men and women tend to go to segregated bathrooms in public places, perhaps there are different social norms for each gender – just as there are for other groups, such as religions.

Rational vs. experiential thinking

One reason scientists are so keen to uncover the psychology behind handwashing is that lives depend on it – especially those of patients in hospital. Despite years of training to keep people alive, many healthcare workers neglect this one basic habit that could help to prevent the spread of potentially lethal viruses and superbugs such as the bacterium Clostridium difficile.

Back in 2007, scientists found that surgeons at an Australian hospital only washed their hands 10% of the time before contact with patients (vs. 30% afterwards). More recent research at other hospitals has uncovered similarly alarming findings. For example, a 2019 study at a hospital in Quebec found that healthcare workers only washed their hands 33% of the time. Even in Saudi Arabia, with its scrupulous culture of handwashing, medical personnel often don’t implement hand hygiene properly.

But as with the general public, not all medical professionals are equally guilty. A 2008 study found that doctors who reported making decisions intuitively were significantly more likely to wash their hands than those who said they thought in a more rational way. This hints that providing a set of arguments for hand washing might not be the best way to convince people to do it.

A study conducted in March this year identified another trait that might be at play: conscientiousness. The research, which was conducted in Brazil, found that people who scored more highly for conscientiousness were more likely to social distance and wash their hands.

Finally, there’s disgust. Your gut reaction to the sight of a maggot-infested steak has the useful side-effect of preventing us from wanting to eat it. Similarly, moving to the opposite end of a train to the passenger clutching a dirty tissue will obviously help us to avoid breathing in their pathogens. “It’s this ‘driving us away’ which is the most helpful thing,” says Dick Stevenson, a psychologist from Macquarie University, Australia.

Even chimpanzees, which are regularly seen eating their own faeces in zoos, are grossed out by the bodily fluids of other individuals – suggesting that disgust is not just a recent byproduct of human culture, but something that evolved to protect us.

And just like every other emotion, the extent to which we experience disgust varies from person to person. It’s a powerful hidden force in our lives, driving our political decisions – people who are more sensitive to disgust are more likely to vote conservative – as well as whether we approve of people being gay, how xenophobic we are, and possibly even how much we fear spiders.

As you might expect, research has consistently shown that people who aren’t so squeamish are less likely to wash their hands, and that when they do, they don’t spend as long under the tap. One study of hand washing in Haiti and Ethiopia found that a person’s knowledge and awareness of health matters weren’t nearly as relevant to whether they washed their hands as the potency of their feelings of disgust.

Keep it clean

So what can be done to overcome these biases?

In the past few weeks, public health bodies, charities, politicians and members of the public have come together to launch arguably the most enthusiastic handwashing campaign in living memory. Celebrities have stepped in to demonstrate proper technique, an abundance of handwashing memes have flooded the internet, and even porn websites have got involved.

Pornhub teamed up with the filmmaker Ani Acopian and producer Suzy Shinn to form Scrubhub – a parody website which exclusively features videos of people washing their hands, with titillating titles such as “Hot Girl Goes Wild in Public in Premium POV – Dirty 2 DISINFECTED!”. This particular video features someone donning a face mask and gloves, applying hand gel and shopping in a supermarket, while observing social distancing rules.

(If you’re in any doubt, the World Health Organization and US Centers for Disease Control and Prevention have released detailed videos and instructions on how people can wash their hands properly.)

But, given what we know about our unhygienic psychological biases, will these well-meaning and sometimes ingenious efforts actually get non-handwashers on board?

Rather than making handwashing amusing or sexy, one major avenue of research is aiming to harness disgust. Back in 2009, together with colleagues from Macquarie University, Stevenson tested the idea on some students. After asking them about their current handwashing habits and disgust sensitivity, they were asked to watch one of three videos: a purely educational video, one with revolting visuals and a control – a clip from an irrelevant nature documentary.

Around a week later, the students were invited back, and sat at a table within reach of antibacterial wipes and alcohol hand gel. They were presented with a series of deeply unhygienic objects to handle – from stained fly swats to used toilet brushes. After holding each object, they were asked to eat a cracker from a plate. Would the volunteers disinfect their hands before touching the food?

As they had hoped, the researchers found that the people who had watched the disgust-inducing video were far more likely to clean their hands than people from the other groups – in fact, they did more hand-cleaning than the other two groups combined.

In a follow-up study, the team confirmed that this could work in the real world, too. By covertly monitoring people’s handwashing in several bathrooms, they found that people were significantly more motivated to do so when they were reminded by posters depicting faeces on a bread roll – to show how germs are spread if you don’t wash your hands – as opposed to purely educational ones.

No one has looked yet to see how long this extra-vigilant handwashing would persist, but it shows that simply telling people to do it is unlikely to be as effective as making them shudder. “This is an important question, because at first you need to keep motivating the person to handwash in particular situations, such as through adverts and signs,” says Stevenson. “But if this is kept up enough then the behaviour becomes a habit. What we don’t know is how long this takes.”

Aunger agrees that this is key. “We have a very special context now, where tonnes of people are interested in handwashing because of coronavirus,” he says. “But the question is, can we get it up to really high levels and keep it there?”

Only time will tell – but at least we’re unlikely to hear any more celebrities bragging about how they don’t wash their hands.

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