Trying to interact with other humans without being able to smile is the facial equivalent of communicating via text message; it’s easy to be misunderstood. Your expression and words lack context. People wonder: Are you wincing at me? Are you grinding your jaw? Do you just have a lot of crow’s-feet? Was what you said an insult or a joke?
According to Paula Niedenthal, a psychologist who heads up the Niedenthal Emotions Lab at the University of Wisconsin–Madison and has studied facial expression extensively, there are three types of smiles: those that express pleasure at a reward or surprise, like when you get to see your friends in person after a prolonged separation (soon, please); those that convey a desire to be friendly, or at least non-threatening, which she calls smiles of affiliation; and those that show dominance, like the one Dirty Harry gives when he asks a certain punk if he feels lucky.
Her studies have shown that it’s harder to tell the difference between affiliative smiles and dominant ones if you can’t see the lower half of the face. In those situations, people have to rely on other clues. She gives the example of walking a dog that suddenly barks at a passerby. A quick look at the unmasked person’s face will confirm whether the passerby is smiling because he thinks he’s much better with his dog than you are or smiling because his dog is also occasionally silly. Behind a mask, this distinction is not so clear.
This article has been excerpted from the original TIME article which you can find in its entirety here.