Environmental sensitivity (referred to as trait sensitivity)—the capacity to perceive and process both

supportive and adverse environmental experiences—may influence adolescent development, yet

evidence in adolescence is scarce compared with that in childhood. We analyzed adolescent

self-reports and maternal ratings from 2,375 Japanese adolescents across three studies. In Studies

1–2, the 21-item Highly Sensitive Child scale showed a bifactor structure (general sensitivity plus

Ease of Excitation–Low Sensory Threshold and Aesthetic Sensitivity), with good internal consistency

and moderate test–retest reliability; trait sensitivity correlated positively with negative emotionality,

behavioral inhibition, neuroticism, and openness. The general sensitivity factor accounted for

approximately half of the variance in the total score. In Study 3 adolescents were followed across

three waves, testing interactions between trait sensitivity and environmental factors (i.e., parent and

peer relationships). No significant interactions were detected; rather, trait sensitivity and environmental

factors showed additive associations with developmental outcomes. Trait sensitivity predicted higher

internalizing problems and greater prosocial behavior. In summary, the psychometric properties of

the HSC-J21 were consistent with those of the original version developed by Weyn et al.