This study examined the association between non-suicidal self-injury (NSSI) and depression in young adults, and tested a serial mediation model in which rejection sensitivity and mistake rumination account for this relationship. A descriptive, cross-sectional correlational design was used with 139 young adults aged 20~34 years who completed validated measures of NSSI, rejection sensitivity, mistake rumination, and depression.
Data were analyzed using SPSS 27.0 and PROCESS macro(Model 6). Results indicated that NSSI was positively correlated with rejection sensitivity, mistake rumination, and depression. The direct effect of NSSI on depression was not significant(β=.12, p=.067), supporting a full mediation model. However, the total indirect effect was significant(B=.28, 95% CI[.18, .39]). Specifically, rejection sensitivity(B=.07, 95% CI[.01, .13]) and mistake rumination(B=.12, 95% CI[.05, .20]) individually mediated the relationship. Furthermore, a significant sequential mediating path was confirmed(B=.10, 95% CI[.05, .16]). These findings suggest that NSSI exacerbates depression by heightening interpersonal sensitivity and triggering self-critical rumination. Given the developmental significance of the transition to adulthood, clinical interventions should target reducing rejection sensitivity and ruminative thought patterns to effectively alleviate depression in this population.