Hurt Others or Hurt Self? Reciprocal Relations Among Neuroticism and Bullying Perpetration/Non-Suicidal Self-Injury Over Time.

School bullying perpetration and non-suicidal self-injury are two major public health challenges in adolescence. The interplay between these behaviors and neuroticism, as well as the underlying mechanisms, has received increasing attention. However, the complex interplay among neuroticism, bullying perpetration and NSSI remains underexplored. Based on this, the present study followed Chinese adolescents (N = 1214; Mage = 15.46, SDage = 0.71; 39.30% girls) across three time points with 6-month intervals. Employing both traditional and random-intercept s, this study sought to elucidate the similarities and differences in the inter- and intra-individual relationships of neuroticism with bullying perpetration and with NSSI in adolescents. Bidirectional relationships were found in the Cross-Lagged Panel Model (CLPM) for all three pathways (neuroticism-bullying perpetration, bullying perpetration-NSSI, and neuroticism-NSSI). However, in the Random Intercept Cross-Lagged Panel Model(RI-CLPM), only the neuroticism-NSSI link remained significant, suggesting it is robust across levels of analysis. The CLPM showed that self-injury not only mediated the link from neuroticism to bullying perpetration, but also exhibited a mutually reinforcing relationship with bullying perpetration. These findings reveal that neuroticism, as a core trait of emotional vulnerability, constitutes a shared psychological root for both non-suicidal self-injury (internalizing aggression) and bullying others (externalizing aggression). This extends prior perspectives that examined internalizing and externalizing aggression separately, offering a reference for understanding the shared psychological underpinnings of these two aggressive manifestations.