Smiles Hide Many Messages—Some Unfriendly

Faces that mean domination, reward or just ‘I want to get along with you’



April 5, 2018 10:20 a.m. ET

See the column on the Wall Street Journal site


Smile while your heart is breaking, put on a happy face, say cheese. We’re so used to smiling on demand that to do otherwise can seem antisocial. Even going through the motions of a smile, scientists have found, can make us feel happy.

But smiles take many forms, and not all of them sound a single, upbeat note. According to recent research, smiles are more like Morse code, silently broadcasting distinct, nuanced messages. A smile might be signaling “Do that again” (reward), “I want to get along with you” (affiliation) or “I’m No. 1 around here” (dominance). Most of us receive these nonverbal signals loud and clear; they register in the chemical cocktail infusing our saliva and the thrum of our heartbeat, says a study published last month in the journal Scientific Reports.

“Different smiles have different impacts on people’s bodies,” said Jared D. Martin, a doctoral student who led the study in the lab of University of Wisconsin psychology professor Paula Niedenthal, working in collaboration with Eva Gilboa-Schechtman of Israel’s Bar-Ilan University. Along with poker players, psychologists have long known that our facial expressions can betray our emotions. But no one has demonstrated exactly how this works, Mr. Martin said.

To explore whether certain types of smiles provoke distinct physiological responses, Mr. Martin’s team set up an experiment based on public speaking. Research shows that most people would rather get zapped with an electric shock than give a five-minute speech about themselves. It’s a handy way to examine how our bodies register stress. So in this experiment, 90 healthy male undergraduate students delivered three spontaneous speeches about themselves, each to an audience of one. The listener smiled away on Skype while they were talking.

That listener was supposedly chosen randomly but in reality was a plant trained to smile in one of three ways during the other’s short spiels: to signal reward, affiliation or dominance. The dominance smile is mildly lopsided, with closed lips and one or both eyes squeezed shut, whereas reward smiles show upturned lips exposing a row of teeth and crinkled eyes. Affiliation smiles feature pursed lips, the whites of the eyes and raised eyebrows.

The research team measured the impact of these three types of smiles by continuously monitoring the speaker’s heart rate and periodically assessing his salivary levels of cortisol, a hormone often used as a marker of stress.

The researchers found that there was eight times as much cortisol in the saliva of students facing a dominance smile as in those facing affiliative smiles and 16 times as much as in those facing reward smiles.

There were also intriguing differences in how people reacted to the different smiles. “Your heart doesn’t beat like a metronome,” Mr. Martin said, and “people with higher variability in their resting heart rate had more extreme cortisol responses to dominance smiles.” These new results are in line with a 2017 German study showing that people with more-variable heart rates are much better at reading others’ mental states in their facial expressions—what psychologists call mind-reading.

The current study tells us that the people with higher heart-rate variability are not only more stressed out by dominance but also more comforted by affiliative smiles. “They’re more attuned,” said Mr. Martin.

The study was on the small side, the subjects restricted to men, and each student received just one type of smile, so the experimenters couldn’t compare how a particular student would respond to different expressions.

But the study helps us to understand the arcane signals exchanged by our intensely social species. The sense of how others view us is read not just by the head but by the hormones coursing through our bodies and the rhythm of our hearts.