Psychologists pinpoint a subtle sign of relationship quality

A recent study published in Emotion reveals a connection between the synchrony of smiles in romantic partners and their overall relationship satisfaction. By examining the timing and coordination of smiles during partner interactions, the researchers discovered that couples who reported high relationship satisfaction exhibited greater levels of smile synchrony compared to couples seeking therapy for relational distress. The findings position smile synchrony as a potential behavioral marker of relationship quality.

Close romantic relationships significantly impact both physical health and psychological well-being. Satisfying partnerships have been linked to benefits such as reduced depression risk and enhanced life satisfaction, whereas distressed relationships may contribute to poor mental health outcomes. Researchers have increasingly explored how emotional processes, such as emotional synchrony, influence the connection between relationship quality and well-being.

Emotional synchrony occurs when partners’ emotional experiences align, whether through shared physiological states or synchronized behaviors. While previous studies have documented synchrony in verbal communication and physiological responses, the role of facial expressions, particularly smiles, had received less attention. Smiles are universally recognized nonverbal signals that convey positive emotions and affiliation, making them an ideal focus for examining emotional synchrony in romantic relationships.

“The inspiration for this research stemmed from a deep curiosity about the world of nonverbal communication between romantic partners,” said study author Reut Machluf-Ruttner, a PhD student at Ben-Gurion University of the Negev.

The researchers recruited 61 cohabiting couples, including 30 nondistressed couples and 31 couples seeking therapy for relationship distress. Nondistressed couples were selected based on high relationship satisfaction scores, while therapy-seeking couples reported satisfaction levels within the clinical range for relational distress. The nondistressed couples were younger, with an average age of 25.6 years for women and 26.4 years for men, whereas the therapy-seeking couples were older, averaging 37 and 39 years, respectively.

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During the study, each couple participated in a laboratory session involving four six-minute discussions. These interactions alternated between positive topics, such as relationship strengths, and negative topics, such as sources of disagreement. The partners’ facial expressions were recorded using high-definition cameras, and their smiles were analyzed using advanced facial recognition software. This software continuously coded the presence and intensity of smiles, allowing the researchers to track the timing and synchrony of smile exchanges between partners.

To quantify smile synchrony, the researchers calculated how closely aligned the timing of partners’ smiles was and how quickly one partner responded with a smile after the other. These measures were compared across nondistressed and therapy-seeking couples, as well as between positive and negative discussion contexts.

The researchers found that nondistressed couples displayed higher levels of smile synchrony, with an average synchrony score of 0.46 (on a scale from 0 to 1) compared to 0.32 for therapy-seeking couples. This means their smiles were more closely aligned in timing and intensity. They also reciprocated each other’s smiles more quickly, achieving their peak synchrony in an average of 0.62 seconds, whereas therapy-seeking couples took 1.07 seconds to reach the same level. These findings suggest that nondistressed couples are more emotionally attuned to each other, while therapy-seeking couples exhibit less alignment in their nonverbal communication.

“Despite being automatic and largely uncontrollable, findings from this study—and others in the field—highlight that these signals are highly indicative and can serve as markers of relationship quality,” Machluf-Ruttner told PsyPost. “In this particular study, we discovered notable differences in the patterns of smile synchrony between couples who are satisfied with their relationships and those seeking therapy due to relationship difficulties.”

Interestingly, smile synchrony was greater during discussions of positive relationship aspects than during negative discussions for both groups. However, the difference was more pronounced in nondistressed couples, who showed faster and more consistent smile coordination during positive interactions. This pattern highlights the importance of emotional connection through smiles, particularly in fostering positive relational dynamics.

The researchers also noted that smile synchrony showed a high degree of consistency across interactions within the same couple, with approximately 45% of the variance in synchrony explained by stable couple-level factors. This stability suggests that smile synchrony may be a characteristic of the relationship itself rather than a fleeting response to specific situational factors, further reinforcing its potential as a marker of relationship quality.

“Currently, I am working on follow-up studies exploring the relationship between couples’ subjective reports of closeness and their facial expression synchrony,” Machluf-Ruttner said. “Additionally, I aim to examine whether smile synchrony might predict which couples are more likely to benefit from couple therapy or from certain approaches to couple therapy. Beyond my research, I am also a clinical psychology intern, and I find the integration of research findings with clinical practice both fascinating and valuable.”

The study, “The Dance of Smiles: Comparing Smile Synchrony in Nondistressed and Therapy-Seeking Couples,” was authored by Reut Machluf-Ruttner, David A. Sbarra, Ben Shahar, Carmel Sofer, and Eran Bar-Kalifa.