2026 POSNA/EPOS Traveling Fellowship Experience.

Nonsuicidal Self-Injury (NSSI) is the deliberate, repeated infliction of bodily harm without suicidal intent—typically cutting, scratching, burning, or hitting oneself (). NSSI disorder (NSSI-D) is listed in Section III of the DSM-5 as a condition warranting further study, defined as self-harm on at least five days within the past year (). A systematic review of longitudinal studies () found that NSSI prevalence peaks at ages 15–16 and declines by age 18. Nevertheless, the behavior remains common, with global prevalence estimates of 16–22% among adolescents (, ), and roughly 13% among young adults (), although data for the latter group are more limited. Importantly, NSSI is not restricted to adolescence, as prior work suggests that NSSI may show a second period of elevated occurrence in emerging adulthood, particularly around the transition to college or university (, ). NSSI is also a significant predictor of later suicide attempts (); for example, Voss et al. () found that two-thirds of individuals who had attempted suicide had previously engaged in NSSI. Clinically, NSSI is seldom isolated; most individuals also meet criteria for depression, anxiety, PTSD, eating disorders, ADHD, or personality disorders (–). Reflecting this transdiagnostic pattern, Lengel et al. () have recently proposed reclassifying NSSI as a clinical specifier rather than a standalone diagnosis to capture its heterogeneity and dimensional nature. Irrespective of diagnostic classification, NSSI is most commonly employed to modulate overwhelming emotion or stress (, ), a function that makes the behavior clinically pressing and highlights the need to understand its underlying mechanisms. Although social and psychological factors associated with NSSI are well studied, and several psychological interventions show promise for reducing adolescent self-harm and related outcomes (, ), the evidence base for interventions specifically targeting NSSI remains comparatively limited. Research on biological underpinnings is still in its infancy. Current pathophysiological models of NSSI () separate distal biological traits—including genetic and epigenetic risk and adverse childhood experiences (ACEs)—from proximal biological traits, such as alterations in brain structure or function and dysregulated stress-response systems. Accumulating evidence shows that exposure to acute or chronic stressors—especially ACEs—heightens the likelihood of NSSI, a link thought to operate through subsequent alterations in neuroendocrine and autonomic stress-response systems (). Experimental work likewise points to dysregulation in the body’s two chief stress systems—the autonomic nervous system (ANS) and the hypothalamic-pituitary-adrenal (HPA) axis—among individuals who self-injure, although the precise role these systems play in everyday NSSI remains unclear (see, , for meta-analyses).