Non-suicidal self-injury (NSSI) consists in the use of non-lethal, self-aimed, deliberate behaviours leading to the destruction of one’s own body tissue, in the absence of the aim to end one’s life (1). It commonly manifests during early adolescence, with an average age of onset between 13 and 16-years-old (2), an age characterised by drastic changes and stressors that can notably facilitate the emergence of personal vulnerabilities and maladaptive strategies. Recent meta-analytic work stated how the occurrence of NSSI behaviour during development shows an initial increase in correspondence of early adolescence, followed by a peak and a subsequent decline (3). Reported data sums up to a relatively high prevalence in this population, estimated to be 16% (4), and, as such, NSSI is identified as a major public health concern (5, 6), even more so as it associates with different negative outcomes, including suicidal behaviours (7). Suicidal behaviours are defined as nonfatal suicidal thoughts and behaviours and classified as a) suicide ideation, the presence of thoughts of ending one’s life; b) suicide plans, the formulation of a specific method to do so; c) suicide attempts (SA), which refer to potentially self-injurious behaviours in which there is at least some intent, overt or inferred, to die (8). These behaviours are well-known harbingers of suicide death in youths, that represent the fourth leading cause of death among 15-19 year olds worldwide (9, 10), with reported global suicide rate amounting to 3.8 per 100,000 people among adolescents (11).

Overall, NSSI can co-occur and precede SA. In fact, 70% of youths with NSSI reported a positive history of at least one SA and a SA risk 3-fold higher than youths without NSSI (12). Therefore, NSSI has been identified as one of the strongest predictors of SA by both cross-sectional and longitudinal studies (13, 14). Despite vast literature on the matter, the etiopathogenesis underpinning this association has yet to be clarified (15, 16). Some neurobiological studies highlighted the role of emotional intelligence and emotional dysregulation (17). Other works have theorised possible facilitating mechanisms underlying both phenomena. Since NSSI was associated with higher lethality of suicide attempts (18), it was theorised that pain desensitisation induced by NSSI could facilitate the enactment of suicidal thoughts (19, 20), leading to an acquired capability to commit SA (21, 22). Other studies hypothesised a psychopathological continuum of self-injurious behaviours with NSSI escalating in SA, particularly when associated with high psychological distress (23, 24). Finally, other authors proposed the role of shared risk factors and, particularly, the identification of specific psycho-social vulnerability domains shared by NSSI and SA (25–27).

In fact, literature seems to point out several areas that could underlie both phenomena, including depressive symptomatology (28–30), dissociative symptoms (31), impulsiveness (31–34), emotion identification (35, 36), expression (37, 38) and dysregulation (39–41), aggressivity and anger pervasiveness (42), feelings of worthlessness (43), and social reactivity (e.g., sensitivity to interpersonal rejection) (44, 45). Despite that, data on possible differences between NSSI and SA relative to these factors is relatively scarce, particularly in youths.

Therefore, our study aimed to investigate the role of a set of psychopathological dimensions in distinguishing between NSSI youths with or without a lifetime history of SA. In particular, our primary aim was to investigate whether current social cognition could discriminate NSSI youths with or without SA, as previous studies suggested its impairment in suicidal attempters (46). Social cognition includes empathy (e.g., the ability to understand the mental states of others and responding to them with affective mobilisation) and the theory of the Mind (ToM), i.e. the ability to infer the emotional states of others based on social cues (47, 48). We specifically explored the affective component of ToM, referring to the understanding of feelings and emotions of others (46). We presume it has a role in suicidality shift in NSSI youths, as it can influence youth engagement in prosocial behaviour, and the development of effective interpersonal communication and interpersonal reactivity/vulnerability. Secondary outcomes investigated whether specific dysfunctional coping patterns, such as emotional dysregulation, anger rumination and self-criticism, could contribute to the development of SA in youth NSSI. Exploratory outcomes included the role of dissociation and alexithymia as precipitating and/or mediating agents for SA among at-risk NSSI youths. The final goal was to preliminarily explore in a sample of youths which variables could help to clinically stratify NSSI youths at-risk for SA, through a pilot study carried out in a real-world setting, ultimately leading to target-specific preventive and treatment programs.

The current study aims to identify a set of psychopathological dimensions between young subjects who manifest only NSSI versus those who display both NSSI and SA, to investigate which vulnerability factors could help stratifying the population of NSSI youths with respect to the risk of presentation of suicidal acts. Our primary objective was to investigate the association between the affective component of ToM and suicidality in a sample presenting NSSI or not. Our findings revealed that NSSIplusSA patients displayed statistically significant higher RMET scores compared to both the NSSInotSA and SAonly groups, while the SAonly group displayed lower scores when compared to the control group. These preliminary findings could potentially suggest that a higher affective ToM may share a distinct, significant relation with suicidality within youth NSSI. Indeed, one could argue that ToM could display different patterns across the lifespan (65) and even more so during adolescence: core features of ToM continue to develop as youngsters are faced with increasingly complex social situations amidst their brain development. Thus, in this paper we hypothesise that a hypertrophic ToM should be further explored as an age-specific marker of suicidality shift within NSSI youths: those with an hypermentalising asset tend to over-interpret information from their social environment about others’ mental states (66, 67). A higher ToM could be maladaptive for interpersonal functioning as it may lead NSSI youths to potentially mistakenly interpret rejection, abandonment or criticism, exacerbating beliefs of burdensomeness and/or lack of connectedness. This could contribute to excessive interpersonal reactivity and social distress, which in turn could determine the transition to suicidal acts. Our findings were also supported by a previous study (68). Interestingly, lower scores at RMET seem to characterise the SAonly group in our sample. This data is coherent with previous literature (36) that suggested how inaccurate mentalising patterns such as lack in others’ emotion recognition seems to be associated with suicidal behaviours. This possibly suggests the presence of different triggering mechanisms and/or underpinned afflictions determining SA in youths with or without NSSI.

A recent meta-analytic work comparing subjects with eating disorders (ED) and NSSI with both a clinical and a healthy control group, found a higher NSSI prevalence in ED subjects, without identifying any significant group-differences on SA (69). Despite our small sample, our findings also partially confirmed this meta-analysis, even though we found a higher comorbid ED diagnosis only in NSSInotSA but not in the NSSIplusSA group. Our results could suggest the possible presence of different subtypes of NSSInjurers, where self-harm as whole could hold a separate meaning and as such it could imply a different likelihood of SA co-occurrence or development. Indeed, these findings should need further replication studies.

Regarding the potential discrimination through dysfunctional coping patterns between the two NSSI groups, our findings did not find any relevant differences in emotional dysregulation dimension. Both NSSInotSA and NSSIplusSA showed significantly higher DERS scores compared to the control group, which is consistent with previous published literature. An association between NSSI and emotion regulation difficulties has been clearly confirmed (40), with NSSI being historically identified as a possible maladaptive strategy to modulate intense emotional reactions (70). Studies on SA and emotion dysregulation, instead, showed contrasting findings (41, 71, 72). Similarly, significant differences regarding the anger-type rumination dimension were not observed, as it resulted significantly higher in all three clinical groups. These findings are consistent with previous literature which supported the presence of a predominant ruminative thought pattern within both NSSI and SA, with self-injury acting as a maladaptive strategy to discontinue highly intensive ruminative cycles (73, 74), particularly in more potentially harmful or dreadful SA (42, 75, 76). Furthermore, interesting findings were observed in the self-criticism dimension, which could partially be associated with those derived by our primary outcome. Although our results observed significantly higher LOSCS scores for both NSSI groups compared to the control group, when we investigated the CSC subscale we found significantly higher scores within NSSInotSA and a subthreshold trend discriminating between two NSSI groups is observed. Indeed, aberrant self-criticism has been described as a facilitator for the development of NSSI and SA (15, 43) as NSSI may represent a sort of self-punishment in response to worthlessness ideation (77, 78), whereas specific types of self-criticism, such as the feeling of an inadequate self with tendency to perfectionism, have been found to increase likelihood of suicidality, both in adult and adolescent samples.

Furthermore, findings relative to exploratory variables warrant for further investigation of dissociative symptomatology. Previous literature already documented the role of dissociative symptomatology in youths with history of NSSI and SA (31, 79), but no discrimination between the NSSI groups (NSSInotSA and NSSIplusSA) was ever suggested. It was proposed that NSSI could act as an “anti-dissociative” (80), while other researchers suggested the presence of a dissociative subtype of NSSI in which self-harm could have a “pro-dissociative function”, as physical pain could facilitate emotional and mental distress anaesthesia (81). Interestingly, the latter has been associated with a shorter shift towards SA (82) and dissociation was suggested as SA facilitator, as it could favour numbness to physical pain and disconnection from one’s body (83), a theory that has been also explored by a study using virtual reality (84). Our findings described significant higher DES-II scores in NSSInotSA and SAonly groups compared to the control group, whereas the NSSIplusSA group showed lower scores, hence suggesting a potential ‘protective’ role of dissociation regarding the presentation of SA among NSSI individuals exclusively. Thus, we suggest that a subtype of NSSI youths at higher risk of suicidality could be identified depending on dissociative dimension.

Overall, despite our exploratory pilot study shedding light on interesting findings, several limitations to the current work should be properly addressed. Firstly, the cross-sectional design precludes causal inferences between ToM and suicidality risk in youth NSSI. Secondly, the relatively small sample prevented us from comparing subgroups and may have invalidated statistical significance where we clearly found a subthreshold trend discriminating between two NSSI groups. Numerosity is particularly relevant in this study as the sample has been divided in 4 groups, thus increasing it could help clarify some borderline situations and reduce statistical error. Moreover, our study did not investigate possible ToM variations determined by age, symptomatology, nor severity of illness. Ultimately, we relied on RMET to preliminarily explore potential variations of ToM: psychometric properties of the test have been recently debated (85), despite the Italian validation study confirming its validity (54). Hence, these limitations contribute to the aforementioned preliminary and pilot nature of the current study, which should be further strengthened by recruiting a larger sample size, including adult subjects, with longitudinal design and a full set of rigorous social cognition assessment tools.

Overall, current findings provide significant implications for future research directions, as well as for timely and target-specific clinical intervention for suicidality risk in youth NSSI. Our primary outcome suggested a role of affective component of ToM in suicidality enactment among NSSI youths. This should be extensively investigated in both clinical and neuroimaging studies, in addition to emotional intelligence, empathy and cognitive components of ToM, to define their role in interpersonal hyper-reactivity which could underpin higher risk to act suicide. Finally, interventional studies should also evaluate which social-cognitive interventions (such as mentalisation-based therapies, cognitive behavioural therapy, etc.) (86, 87) could effectively address this hypermentalising dimension in at-risk youths, possibly aiming at the reduction of social sensitivity-induced distress and implementation of more functional interpersonal strategies.

The datasets presented in this article are not readily available because of identifiable participants’ data. Requests to access the datasets should be directed to l.orsolini@staff.univpm.it.

The studies involving humans were approved by Local Institutional Review Board. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants’ legal guardians/next of kin.

LO: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Methodology, Conceptualization. DC: Writing – original draft, Investigation, Formal analysis, Data curation. AC: Writing – review & editing, Investigation, Data curation. ER: Writing – review & editing, Supervision, Investigation, Data curation. GL: Resources, Writing – review & editing, Visualization. UV: Writing – review & editing, Visualization, Validation, Supervision.