A Smile That Convinces: How a Smile Shapes Our Relationships of Trust

This study shows that smiling, even unconsciously, can make us trust other people more. By automatically imitating someone's smile, our brain "incorporates" that emotion, which increases the perception that this person is trustworthy. Researchers have demonstrated that this effect is not just a subjective impression: the physical act of smiling itself influences our judgments and even our trust decisions in real-life situations. Thus, facial mimicry acts as a powerful social glue in human interactions.

You've probably experienced the following situation: someone smiles at you and, almost automatically, you smile back, even without realizing it. This common and seemingly simple behavior is called emotional mimicry. It happens when we unconsciously copy the facial expressions of the people around us.

This type of imitation is not just a polite social gesture, but is part of a set of deep mechanisms that shape how we relate to and interpret others.

The study in question starts precisely from this everyday observation to investigate something bigger: does imitating someone's facial expression, especially a smile, really change the way we judge that person? More specifically, does copying someone's smile make us see them as more trustworthy?

To answer this question, the researchers conducted a series of carefully planned experiments. In them, volunteers watched short videos showing faces of different people expressing three basic emotions: happiness, sadness, or anger.

While participants watched these videos, scientists used a technique called facial electromyography, or EMG. This technique measures extremely subtle electrical signals generated by the facial muscles, signals so small that they normally go unnoticed. This made it possible to precisely identify whether the participants were, even unknowingly, activating the same facial muscles as the people appearing in the videos, that is, whether they were imitating those expressions.

After watching the videos, participants were asked to rate the people they had seen based on important social characteristics, such as how trustworthy, attractive, or confident they seemed. In an even more concrete stage of the study, trust was measured not only by opinion but also by real behavior.

Participants took part in a so-called "investment game" or "trust game," in which they had to decide how many virtual points they were willing to share with the person in the video. The more points shared, the higher the level of trust demonstrated in practice.

The results were very consistent and revealing. Researchers observed that the more intensely a person imitated the smile seen in the video, even unconsciously, the greater the trust they placed in that person. In other words, it wasn't just seeing someone smile that mattered, but how much the observer's own face entered into this "game" of imitation.

More than a simple association, the study managed to demonstrate a causal relationship: the physical act of smiling, even if involuntary, directly helps to generate feelings of trust. In other words, the body not only reflects what we feel, it also helps to create what we feel.

This discovery is especially important because it offers a scientific explanation for something that popular wisdom has long suggested: the idea that smiling facilitates relationships. The study shows that the positive sensations we have when interacting with someone smiling are not vague or purely emotional.

They are linked to well-defined physical and neurological processes, in which our brain "incorporates" the emotion it observes in the other person through the activation of facial muscles. This mechanism causes the emotion seen externally to be, in part, felt internally.

Emotional mimicry, in this context, functions as a true social glue. By subtly mirroring someone's happiness, we send signals that we are friendly, approachable, and non-threatening. At the same time, this imitation influences our own brain, increasing our sense of security and trust in that person. This process helps explain why trust arises more easily in warm and positive interactions, even between strangers.

Understanding this mechanism is fundamental because trust is at the base of virtually all human relationships. It sustains friendships, family ties, professional partnerships, doctor-patient relationships, educational interactions, and even political and diplomatic negotiations.

The study also shows how simple nonverbal cues, such as facial expressions, can create a positive feedback loop in social interactions. A smile generates imitation, imitation generates trust, and trust strengthens the connection between people.

Additional experiments further deepened this understanding. In one of them, researchers asked participants to perform specific facial movements while assessing the trustworthiness of other people. These movements could facilitate or hinder the activation of the muscles involved in smiling.

When muscle activity associated with happiness was stimulated, reliability ratings increased. When this activity was inhibited, positive perceptions decreased. This reinforced the idea that it's not just about observing emotions, but about experiencing them physically through one's own body.

The study also showed that not all emotions function the same way in this process. Imitating sadness, for example, was associated with lower levels of trust in some experiments, although this relationship was not clearly causal. Anger, on the other hand, was the least imitated emotion, suggesting that we tend to more easily copy expressions that signal affection and connection, such as happiness and sadness, than expressions of confrontation or threat.

Overall, these results offer solid evidence that facial mimicry plays an active role in how we evaluate others and attribute social traits, such as trustworthiness. Far from being purely rational judgments, these evaluations are profoundly influenced by automatic bodily processes.

Thus, the study reinforces the idea that our social interactions don't just happen "from the head out," but involve a constant integration between body, brain, and environment. Ultimately, it shows that something as simple as a shared smile can be the first step in building trust.

READ MORE:

Smile and the world smiles (and trusts) with you: Happiness mimicry shapes first impressions.

Olszanowski M., Tołopiło A., and Hess U. 

APA PsycArticles: Emotion. Advance online publication. 2025

https://doi.org/10.1037/emo0001586

Abstract|:

Numerous studies have shown that the processes underlying trait judgments can be influenced by concurrent affect processing. The present project explores the role of emotional mimicry in trait attribution. Across three experiments, we asked participants to assess social characteristics of faces expressing happiness, sadness, and anger. In Experiments 1 and 3, we used facial electromyography to predict participants’ inferences about trustworthiness, confidence, and attractiveness (Experiment 1) or their behaviorally assessed trust by asking participants to share virtual points in a “trust/investment game” (Experiment 3). In Experiment 2, we tested the causal relationship between facial activity and trait judgments. Participants were asked to assess trustworthiness while performing facial movements that either enhanced or inhibited muscle activity during mimicry of given emotional expressions. The results indicate that mimicry of happiness not only predicts but is causally linked to perceptions of trustworthiness—the stronger the imitation, the more positive the assessments. The results of Experiments 1 and 3 show that increased sadness mimicry is associated with lower trust ratings, although the results of Experiment 2 do not support a causal relationship. Additionally, we confirmed previous observations that people are more likely to mimic affiliative displays (i.e., happiness and sadness) than antagonistic ones (i.e., anger), with happiness being the most likely to be mimicked. In summary, these studies provide evidence that facial mimicry modulates social trait inferences and underscores the functional role of mimicry in social interactions. (PsycInfo Database Record (c) 2025 APA, all rights reserved)