Science

The Surprising Truth and Fascinating Science Behind Smiles

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Those facial expressions we make when we’re happy or pleased have a surprisingly hefty influence on everything from our intelligence to our longevity to our drinking habits. Here’s what smiles really mean, what we’ve learned from two years of hiding them, and why now may be the perfect time to fix yours.


My daughter Marcy was in high school when her course of orthodontia went seriously awry, resulting in the loss of two of her front teeth. What followed was a years-long lesson in consultations, operations, pain meds and teen regret. The missing teeth couldn’t be replaced by implants until Marcy was done growing, so she wore a little plate thing with fake teeth in it all through the rest of her high-school years and into college. And she became hyper-sensitive about her smile, frequently hiding it, shy Lady Di-style, behind a raised hand. 

She also didn’t enjoy college, once she went. She always felt out of place; the tony private school that seemed so perfect for her when we chose it turned out to be filled with kids who had a lot more money and way better teeth than she did. But I never connected her dental tribulations with her college experience until I read the research conducted by Temple University psychology professor Kareem Johnson.

Johnson has spent probably as much time as anybody on earth thinking about smiles. Studies he conducted early in his career focused on the interplay between emotional states and cognitive ­processes — how the way we feel affects the way we think. And it turns out that a smile is surprisingly powerful, which is one good argument for taking care of yours.

Scientists theorize that the human smile evolved as a sign of submission. In most animals, baring the teeth — think of a lion or dog — is a warning: Back off or else! That’s true of primates, too, so long as the lips are curled backward and the teeth are parted. But relax those lips and put the teeth together, and an orangutan or chimp is signaling submission: I’m no threat! You’re in charge! (Interestingly, this behavior is innate; babies who are born blind smile just like the rest of us do.)

But not all smiles are created equal. For decades, researchers have distinguished between forced or fake smiles and the real thing, sometimes called a “Duchenne smile” thanks to 19th-century French anatomist Guillaume Duchenne, who studied facial musculature. (In most Romance, Celtic and Slavic languages, delightfully, the word for “smile” is a diminutive form of the verb “to laugh.”) Duchenne found actual differences between smiles that engage the orbicularis oculi muscles surrounding the eyes and those that don’t. The former are involuntary, arising spontaneously out of enjoyment or amusement; the latter are the posed, false smiles we make when we’re ordered to say cheese or have our driver’s-license photos taken. These two types of smiles involve two different neural pathways. A good example of a non-Duchenne smile is what Johnson calls “hallway smiles” — those little grins you give when you pass colleagues in your workplace. (Well, back when we had workplaces.) Positive emotional changes, Johnson explains, are an involuntary response to a Duchenne smile. And those emotional changes cause mental changes: “That doesn’t happen with a polite smile.”

This isn’t surprising; emotions in general are contagious, so we recognize them in others when we see them, and we tend to mirror them back. “Each emotion has a different job to do,” Johnson says. “Take fear. Fear’s job is to keep you alive.” When we’re scared, our blood flow increases and rushes to our muscles, so we can flee if we have to. Our eyes scan our surroundings for threats and avenues of escape. That’s the reason, Johnson says, that eyewitness testimony is so notoriously unreliable. Remember author Alice Sebold’s erroneous identification of recently freed Anthony J. Broadwater as her rapist? Her mistake isn’t unusual; faulty eyewitness testimony is involved in three-quarters of court cases where DNA evidence later leads to exoneration. “When you’re scared,” Johnson says, “your focus is on the weapon, not on the person’s face or clothes.”

Positive emotions, on the other hand, Johnson’s research has shown, help us in the long term. “They make us more creative, more flexible, more socially inclusive,” he explains. “If we’re at a party where we don’t know anybody and people are laughing, we feel closer to them. Smiles lower the us-vs.-them mental processes, so you see the face, the individual, and not the group.” Think of that old song that goes, “When you’re smiling, the whole world smiles with you.” Remarkably, one of Johnson’s earliest studies, in 2005, showed that viewing videos that elicited a joyful response made white students better able to recognize Black faces, serving to lessen what scientists call the “own-race bias” springing from our tendency to see people in terms of race rather than as individuals. 

Never underestimate the power of a smile.

While humans aren’t the only animals that grin — ­Johnson notes that chimps smile with pleasure and laugh when ­tickled — there are some intriguing differences in how and when we smile. Women, for example, smile an average of 62 times a day, vs. a mere eight times for men. (According to the Yale study that pinpointed this, the difference can be laid down to a smorgasbord of factors, from cultural influences to gender norms to social position. The gap is more marked when we’re young and narrows as we age. “Women do what we call ‘emotional work,’” psychology professor Marianne LaFrance, senior author of the study, explained, “and one of the best ways to do this is to smile to soothe hurt feelings, to restore harmony.”) The more culturally heterogenous a geographic region is, the more its inhabitants smile; it seems that in areas with higher levels of immigration and assimilation, we flash that “Not a threat!” message more spontaneously. But Duchenne smiles are especially powerful. Women who were judged to be showing these smiles in their college yearbook photos — which provide a handy historical source — were more likely to marry, to stay married, and to enjoy greater marital satisfaction than those whose smiles were deemed forced. (That study controlled for attractiveness, so it’s not just that hotties were happier.) Ominously, a 2019 study showed that workers with public-facing jobs, like waiters, sales reps and nurses, are more likely to be problem drinkers than other kinds of employees. After testing various hypotheses for their results, the researchers concluded it was the emotional labor of such jobs — “effortfully amplifying, faking, and suppressing emotional expressions” — that drove employees to tipple. 

Yet there’s some evidence that making your muscles form even artificial smiles can be beneficial. In an ingenious experiment, Dutch researchers had subjects evaluate the facial expressions of others under two sets of conditions: while the subjects were holding a pen horizontally in their mouths, and while they weren’t. In the former case — try it yourself! — the evaluator’s facial muscles are pushed up into a grin. And clenching pens in their teeth caused the subjects to rate others’ facial expressions more positively. “When your muscles say you’re happy,” lead researcher Fernando ­Marmolejo-Ramos reported, “you’re more likely to view the world in a positive way.” That study and a successful replication are reinforced by a Welsh study showing that women whose ability to frown is hampered by Botox injections report feeling happier and less anxious than those who haven’t been Botoxed — even though the former didn’t feel any more physically attractive than their counterparts. 

While past studies have tended to focus on the effects of negative emotional states, examining positivity has yielded some truly startling results. One of Kareem Johnson’s experiments showed that frequent Duchenne smiling actually makes us smarter — more attentive to our surroundings, better at task performance. That study concludes that smiling isn’t just a matter of seeing the world through those metaphoric rose-colored lenses; rather, by “promoting broader perspectives and more flexible thinking,” it “seeds an expansive mind-set that may be a vital contributor to health and well-being over the long term.” 

In some senses, Johnson acknowledges, his work seems to reinforce Norman Vincent Peale’s hackneyed concept of “the power of positive thinking.” But Peale’s focus was always on self-help, not on society. It’s the actual feeling of happiness or joy, Johnson says, that alters your mental state: “A smile changes your attention so you have a literal big-picture perspective. Some of the benefits of positive emotions are to help undo the lingering effects of negative emotions like close-mindedness and self-protection.” In other words, a simple smile makes us better citizens.

And just what, you may ask, does all this have to do with dentists? When Johnson was nine or 10, he broke two front teeth — in his case, in a swimming accident. He had crowns put in, but in grad school, they broke. Just like Marcy in college, “I remember not wanting to smile,” he says, “so people wouldn’t see my messed-up teeth.” When you don’t smile, you don’t just lose the physical and mental benefits thereof; you also don’t see the smiles of others reflected back at you: “It’s absolutely connected.” Not smiling literally changes how you view the world. So if a fear of dentists or wanting to avoid the bother of dental work hampers your smiling, you might want to reconsider. 

Which brings us to the matter of masks. 

Thanks to COVID, my two-year-old granddaughter wears masks perfectly ­cheerfully — at preschool, at the grocery store, even at home if visitors come by. My pandemic walks take me past a middle school nearly every day, and I see the same thing — young people pouring from the building and setting out for home still wearing their masks. If smiling is so important to how we read and interpret the world, I can’t help but wonder: What effect will widespread (at least among sensible people, even the two-year-olds) masking have on kids growing up in these dark days?

Kareem Johnson wonders the same thing. It’s harder to read the expressions of others when they’re masked, he acknowledges. “My big concern is that children are being deprived of seeing the real smiles of adults,” he says. “We’ll have to wait and see how it affects them.” Fortunately, he notes, “There’s more to a smile than just the bottom half of the face. The story is told by the eyes, not the mouth.” I’ve noticed this while shopping; if a kid in a neighboring cart amuses me, his parent can almost always tell I’m smiling in appreciation beneath my mask, not cursing under my breath. I’ve also found my gaze will linger longer on the parent than it might were we not trying to gauge each other’s mood. We have a shared moment, if you will. Johnson isn’t surprised. “Especially with strangers, you see the eyes scrunch up,” he says. “You see body-­positive changes that are inviting. ‘Submissive’ is the wrong term, but you bow a little, you know? You lean toward them a bit.” 

He also notes the encouraging example of places like Japan where mask-wearing has long been more common than it is here. The residents there aren’t any less charitable than Americans simply because they see fewer faces. “They wear masks as a courtesy to the community,” he says. “If someone has a cold, they put on a mask. They’re trying to prevent disease. The culture is more attuned to the good of the group” — which is hardly a bad thing. 

And, interestingly, a study published late last year showed that wearing a mask increases the actions of the good old orbicularis oculi, the definer of that Duchenne smile. Already, it seems, we’re compensating for the potential loss in communication the pandemic has caused. So keep on wearing that mask, and focus on how glorious it will be when we all unveil our choppers again. And if, by chance, the state of your teeth has been causing you to smile less than, say, a Julia Roberts mouth would, it may be time to think about having that faulty feature fixed — if not for society at large, then strictly for yourself. A 2011 study of the smiles of pro baseball players found that smile intensity was actually linked to longevity; the players who showed Duchenne smiles in their yearbook photos were half as likely to die in any given year as those who didn’t. Surely that’s worth bracing yourself. 

These celebrity grins were deemed by science to be superior smiles. / Photographs via Getty Images

Million Dollar Mouths

Do the yappers above look familiar? They should. Online search service Expressdentist.com assembled a list of top-earning actors and subjected their photos to a scrupulously scientific (!) assessment that rated the comparative whiteness of their choppers as well as their smiles’ adherence to Euclid’s renowned “golden ratio,” which has something to do with height vs. width and involves numbers, so … who knows? Our grid shows eight of the 20 top-ranked grins. Try and match the winning mouths to the names; answers below!

Choose from:

Ben Affleck; Emily Blunt; Jackie Chan; Vin Diesel; Gal Godot; Scarlett Johansson; The Rock, a.k.a. Dwayne Johnson; Angelina Jolie; Nicole Kidman; Akshay Kumar;Melissa McCarthy; Lin-Manuel Miranda; Elisabeth Moss; Ellen Pompeo; Adam Sandler; Will Smith; Meryl Streep; Sofia Vergara;Mark Wahlberg.  

Answers to the Grin Quiz

1. Will Smith; 2. Sofia Vergara; 3. Lin-Manuel Miranda; 4. Scarlett Johansson; 5. The Rock, a.k.a. Dwayne Johnson; 6. Melissa McCarthy; 7. Adam Sandler; 8. Gal Godot.

Published as “What’s in a Smile?” in the March issue of Philadelphia magazine.

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