Mar 10, 2020 7:00 AM

Can't Stop Touching Your Face? Science Has Some Theories Why

Ground squirrels do it. So do human fetuses. How did we all end up with this unhygienic habit?

By now the message should be clear: Your hands are not your friends. Public health officials have told us repeatedly that putting your fingers near your eyes and mouth offers easy access to the new coronavirus. But they know it isn’t easy to follow this advice. (They can’t even follow it themselves.) One small study found that medical students, who really must know better, touched their faces an average of 23 times per hour during a lecture, or once every 2.5 minutes. This finding, like many others one can find in medical journals, makes a simple and prescriptive point: It tells us that we’re all a bunch of dirty self-inoculators, in the hopes of getting us to stop. But there’s another body of research into this same behavior, and one that tries to touch on deeper questions of its origins: Could there be an evolutionary basis among human beings (and our kindred species) for this unhygienic quirk? Might the rubbing of one’s face with germy digits come from primal urges that blossomed on our branch of the tree of life?

We do know it’s likely you’ve been pawing at your face since before you were even born. The well-established fact that fetuses will, in utero, touch their fetal hands to fetal faces has led to scientific inquiry. One recent study conducted ultrasounds on 15 women from week 24 to week 36 of their pregnancies and found that fetuses were more likely to touch their faces with their left hands when the women reported feeling stressed. The same researchers published another small study hinting that the fetuses of women who smoke cigarettes might be more likely to touch their faces than those of nonsmoking women, although that finding was not statistically significant.

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The idea that stress fuels a face-touching urge has some backup from research into grownups. A study in Germany analyzed the electrical brain activity of 10 young adults while they completed a memory test, as unpleasant sounds were blasted at them from a loudspeaker. An association between the stressful sounds and volunteers’ grabbing (with either hand) at the nose, cheeks, or chin—as well as subsequent changes in their brain activity—led the study’s authors to to speculate that “spontaneous facial self-touch” helps people to regulate emotions. How might these results fit with those above, where fetuses with stressed mums face-touched with their left hands in particular? That remains a head-scratcher. (Please don’t really scratch your head.)

Clearly this behavior isn’t limited to humans. If you’ve never seen a dog cover its nose with a forelimb or a sleeping cat covering its eyes with its paws, then navigate your way to the nearest online stream of adorable animal memes. As is the case with humans, though, exactly why our furry, mammalian friends touch their faces remains difficult to decipher. One detailed study of self-grooming by ground squirrels published in the 1970s asserted that the animals’ “face washing” could be a scent-related behavior. The author noticed that the squirrels “washed” their faces with their forepaws, and that males would often do this before pouncing on other males in a fight. This, he thought, might be an action to help the rodents spread scents around their body from secretory glands.

We don’t think about humans passing scents to one another, let alone rubbing their faces for that purpose, but a preliminary study suggests that face-touching may serve a social purpose for us, too. In a 2015 paper published in the journal eLife, Israeli scientists hooked up volunteers to devices that measured the air flow through the nose. They didn’t tell the participants the reason for this, and secretly filmed the volunteers meeting people and shaking hands. The experiment showed that volunteers often brought their hands to their noses after shaking hands with other people of the same gender. And when they did so, the airflow through their noses doubled. According to the scientists, this suggests that the subjects weren’t scratching an itch but instead testing the scents of the people they had met. Of course these days it might be more difficult to do the same, since we’ve been advised against shaking hands altogether.

The evolution of face-touching is not a new mystery, but it’s an elusive one to crack. One highly cited paper from 1984 suggested that among primates, including humans, the left hand was more prone to touch the face than the right hand. This, they guessed, rather wildly, was so that the left hand could act as a pointer to emotions on the left side of the face that originated in the right side of the brain. That paper tried to connect a lot of loose dots, but its major findings (let alone its theories) haven’t been borne out. Case in point: The authors of the 1984 paper suggested that gorillas, orangutans, and chimpanzees touched their faces as often as humans do, whereas monkeys “show little if any face touching” at all. Followup studies did not agree with that: Macaques seem to touch their face too—and they do it a lot. (The later research also disputed the idea that face-touching among primates is primarily left-handed.)

There’s a lot of food for thought, though: A psychiatrist writing in 1970 about a patient who had a habit of touching himself on the face, particularly around his mouth, noted that “mouth-hand actions are coordinated during the first month in infancy as seen in association with the feeding process.” More recent research has tried to measure how babies’ faces receive sensory feedback, and how this can facilitate feeding. Scientists developed tools to measure brain waves from premature infants when they are touched on the face, and concluded that this sensory ability “is critical for breastfeeding in the first days of life.” Interestingly, the same researchers who ultimately uncovered hints in ultrasound images that fetuses might touch their faces with their left hands when moms-to-be are stressed also found evidence suggesting that fetuses in later stages of development open their mouths in anticipation of touching their mouth areas. The authors have wondered if this behavior in utero could be an indicator of brain development necessary for the healthy development of feeding behavior.

That fetuses and newborns should touch their faces as they get familiar with their mouths makes sense, but why do we continue to pull at the corners of our mouths in adulthood? Our bulging waistlines are evidence that we know perfectly well how to eat. Could it be that when we tug at the corners of our mouths or cover our eyes with our fingers we are tapping into an ancient tendency, shared with other species? It’s tempting to look around and see the possibilities. Take, for example, a report from a decade ago that a group of English mandrill monkeys in a zoo in Colchester, England, had started doing facepalms. When you read about the mismanagement of the current Covid-19 epidemic by White House officials, you’re likely to start making the same gesture.

Updated 3/10/20: This story has been corrected to reflect that medical students were found to touch their faces once every once every 2.5 minutes, not seconds, as previously stated. This was an error in editing.