Loneliness modulates social threat detection in daily life.

Loneliness is increasingly recognized not only as a stable trait but also as a dynamic affective process, marked by short-term fluctuations in mood, social perception, and behavior. This study examined how self-reported experiences of loneliness, perceived rejection, and social behavior unfold across time in daily life. A community sample of 157 midlife adults completed ecological momentary assessments five times daily for 20 days, reporting on feelings of loneliness, social threat, self-disclosure, and interaction frequency. Dynamic structural equation and multilevel models demonstrated reciprocal associations between momentary loneliness and perceived rejection. Greater variability in loneliness was associated with more unstable threat appraisals, and increases in loneliness predicted subsequent reductions in both social interaction and self-disclosure. These within-person dynamics were moderated by trait loneliness: individuals higher in trait loneliness exhibited more persistent loneliness, stronger coupling between loneliness and perceived rejection, and greater social withdrawal. Findings support a multi-timescale framework in which recursive patterns of emotion, perception, and behavior contribute to the maintenance of loneliness in everyday life.