Non-suicidal self-injury (NSSI), defined as the deliberate destruction or alteration of body tissue without conscious suicidal intent, is increasingly recognized as a major public health concern. The concept and assessment of NSSI has also evolved in recent years, and it is even listed as a distinct syndrome in the DSM-Ⅴ "Conditions for Further Research"[1]. This NSSI behavior most often occurs during adolescence[2] and has a high prevalence in both clinical and epidemiological samples. A recent longitudinal study of non-clinical adolescents reported a prevalence rate of over 17.2%[3]. Moreover, NSSI is both a risk factor for suicide and mental health problems such as depression and anxiety in the near-term[4–6] as well as a longer-term risk factor for more severe mental illness and suicide[7]. Therefore, identifying the risk factors for NSSI in adolescents will provide valuable clues to etiology and effective interventions.
According to the empirical avoidance model, adolescents exhibiting NSSI have stronger emotional experiences, poorer emotional regulation, and a greater propensity for avoidance behaviors, especially avoidance behaviors meant to relieve or provide a distraction from emotional pain( including the physical pain generated by NSSI ). Moreover, this avoidance behavior can increase over time[8, 9]. In contrast, other theoretical models posit interpersonal motivations for NSSI, such as changing the external environment and influencing others[10, 11]. For instance, Nock proposed a social theory in which NSSI is aimed at conveying emotional pain, eliciting caring and supportive responses, and strengthening relationships[12]. However, it is generally accepted that emotional regulation is the most common motivation for NSSI. Moreover, Turner and coworkers demonstrated that NSSI is associated with emotional regulation disorders[13].
Borderline personality disorder (BPD) is a severe mental disorder characterized by emotional instability, intense and volatile relationships, impulsivity, distorted or fragile self-image, paranoia, and frequent suicidal ideation[14]. The biosocial theory of BPD[15–17] proposes that emotional deficits, such as hypersensitivity, over-reactivity, a tendency for the physiological responses associated with emotion to recover slowly, and defects of emotional regulation are core disease characteristics. While BPD is usually diagnosed in young adults, Crick et al. concluded that some adolescents exhibit relatively stable cognitive, emotional, and behavioral characteristics similar to those of adult BPD patients, and coined the term adolescent marginal personality feature (BPF)[18]. Subsequent studies on adolescent BPF found a higher risk of suicide, NSSI, and substance abuse as well as frequent risk-taking behaviors, seriously impaired social function, and poor overall mental health[19]. Given the high prevalence of BPF and its potentially devastating consequences on physical and mental health among adolescents, there is an urgent need to identify associated risk factors than can enhance prevention and early intervention efforts[20].
Previous studies have examined the associations of NSSI with BPF and emotional regulation. However, NSSI is also frequently observed in depression, which is the most prevalent psychiatric disorder among adolescents globally and a major risk factor for suicidality. Therefore, the current study examined the associations among BPF symptoms (emotional instability, identity disorder, poor family relations, negative emotion regulation, cognitive reappraisal, and expression suppression) and NSSI in adolescent patients with depression, and explored whether emotional regulation plays a mediating role between borderline personality traits and NSSI.