Daily manifestations of maladaptive personality traits and loneliness across social contexts in youth.

Adolescence is characterized by heightened sensitivity to social belonging, making loneliness prevalent and consequential for youth. Maladaptive personality traits may further exacerbate loneliness. In this preregistered 14-day Ecological Momentary Assessment study, we examined loneliness across social contexts and timescales in relation to maladaptive personality traits among N = 294 adolescents aged 12-21 years (M age = 17.5, SD = 2.64; 58.5% female; 86.73% born in Germany). Participants answered 27,503 of 32,340 momentary prompts, indicating high compliance (85.1%). Loneliness (β momentary = 0.51; β daily = 0.67) was higher when participants were alone, yet only the presence of close others (e.g., friends) - not weaker ties (e.g., classmates) - reduced loneliness (β = -0.39 to -0.62). Youth who were alone more frequently did not report higher overall loneliness. Maladaptive personality traits were associated with higher (β momentary = 0.32; β end-of-day = 0.40) and more variable (β momentary = 0.31; β end-of-day = 0.34) loneliness but amplified the effect of being alone on loneliness only on the between-person level (β = -1.13). Exploratory analyses indicated that social satisfaction partially mediated the association (β = 0.50). These findings underscore the importance of both structural and qualitative aspects of social environments, as well as personality-related vulnerabilities, to better understand loneliness dynamics in youth.