If you’re looking for a foolproof lie detector, the face isn’t it. According to research, even the most experienced law enforcement officials only spot liars about half the time. Nevertheless, there have been studies that revealed smile patterns among people who were actively trying to deceive others in high-stakes situations. A 2012 study conducted a frame-by-frame analysis of people filmed while publicly pleading for the return of a missing family member. Half of those individuals were later convicted of killing the relative. Among the deceivers, the zygomaticus major muscle — the one that pulls your lips into a smile — repeatedly fired. Not so with those who were genuinely grief-stricken.
People sometimes smile to show their superiority, to communicate contempt or derision, and to make others feel less powerful. You might call it a sneer. The mechanics of a dominance smile are different than reward or affiliative smiles. A dominance smile is more likely to be asymmetrical: One side of the mouth rises, and the other side remains in place or pulls downward. In addition to these movements, dominance smiles may also include a lip curl and the raising of an eyebrow to expose more of the white part of the eye, both of which are powerful signals of disgust and anger. Studies show that the dominance smile works. ResearchersTrusted Source tested the saliva of people on the receiving end of a dominance smile and found higher levels of cortisol, the stress hormone, for up to 30 minutes after the negative encounter. The study also found that the sneer raised heart rates among the participants. This kind of smile is a nonverbal threat, and the body responds accordingly.
People also use smiles to reassure others, to be polite, and to communicate trustworthiness, belonging, and good intentions. Smiles like these have been characterized as “affiliation” smiles because they function as social connectors. A gentle smile is often perceived as a sign of compassionTrusted Source, for example. These smiles involve the upward pull of the lips, and according to researchers, often trigger dimpling in the cheeks. According to research, affiliative smiles can also include a lip pressor, where the lips remain closed during the smile. Keeping the teeth hidden might be a subtle reversal of the primitive tooth-baring aggression signal.
Many smiles arise from a positive feeling — contentment, approval, or even happiness in the midst of sorrow. Researchers describe these as “reward” smiles because we use them to motivate ourselves or other people. Reward smiles involve a lot of sensory stimuli. Muscles in the mouth and cheeks are both activated, as are muscles in the eye and brow areas. More positive input from the senses increases the good feelings and leads to better reinforcement of the behavior. For exampleTrusted Source, when a baby unexpectedly smiles at their mother, it triggers the dopamine reward centers in the mother’s brain. (Dopamine is a feel-good chemical.) The mother is thus rewarded for her baby’s apparent happiness.
The Pan Am smile gets its name from the Pan Am flight attendants who were required to keep smiling, even when customers and circumstances made them want to throw peanut packets across the cabin. Widely regarded as forced and fake, the Pan Am smile might have appeared extreme. Studies show that when people are posing, they use extra effort to yank on their zygomaticus major muscle. As a result, the corners of the mouth are extra high, and more of the teeth are exposed. If a posed smile is asymmetrical, the left side of the mouth will be higher than the right side. If you’re one of the nearly 2.8 million people employed in the customer service industry, or if your job requires you to interact regularly with the public, you might want to reconsider relentlessly deploying the Pan Am smile, as it could affect your health. A recent study published in the Journal of Occupational Health Psychology found that people who have to fake happiness regularly at work often end up drinking off the stress after they clock out.