With the growing scientific interest in self-harm, studies have been conducted to identify risk factors for self-harm. Childhood adverse experiences, such as sexual and physical abuse, emotional neglect, and unstable attachment, were associated with selfharm in later life [1,2]. Community-based study also reported that poor family function mediates the association between childhood adversity and nonsuicidal self-injury (NSSI) in adolescence [3]. In a study of hospitalized adolescents, negative life events were associated with increased chances of NSSI occurrence [4], and a meta-analysis of 21 studies reported that there was a significant correlation between life stress and NSSI [5]. Furthermore, a study of adolescents in ten European countries showed an association between bullying and self-harm [6], and a significant association between NSSI and bullying was reported by a metaanalysis of nine studies [7].

Many studies have focused on the relationship between self-harm and suicide. Suicidal thoughts and behaviors are more likely to follow self-injurious thoughts and behaviors [8,9]. Self-harm is a major risk factor for suicide, and researchers have found that suicide rates are significantly high in the first year after self-harm occurs [10]. More than half of those who died by suicide had a history of self-harm [11], and NSSI before the age of 18 has been associated with a higher likelihood of future suicide attempts (SAs) [12,13]. Suicidal risk has been shown to increase with the presence of comorbid mental illness or repetitive self-harm [14], and frequent self-harm has been associated with the presence of mental illness [15].

In a previous study on community populations in Korea [16], 13.8% of middle and high school students reported having injured themselves in the past year, which is comparable to the 12-month incidence in Europe and the United States [17]. Another research on the middle school students in Korea found that 12.4% of the students had self-harmed at least once and that the self-harm group had significantly higher levels of academic stress, alexithymia, depression, and difficult relationships with parents and peers [18]. In a study of risk factors for NSSI in adolescent depressed patients, researchers found that the self-harm group had significantly higher levels of anxiety, suicidal ideation, and emotional and physical abuse [19].

Although several investigations have identified clinical characteristics associated with self-harm, the previous studies have limitations in that they targeted the community populations or adolescents with specific psychiatric diseases. Moreover, most of the studies used the dichotomous definition of self-harm behavior as NSSI or SA. Therefore, it is necessary to investigate clinical factors associated with the broad concept of self-harm regardless of suicidal intent and whether the clinical factors are different between NSSI and suicidal behavior in Diagnostic and Statistical Manual of Mental Disorders (DSM)-5, in the clinical population.

Therefore, the purpose of this study was to compare the clinical and psychosocial characteristics of psychiatric adolescent inpatients at Samsung Medical Center, a university hospital based on the presence of self-harm and to examine the factors that predict selfharm. Furthermore, we investigated whether clinical factors were significantly different when divided into NSSI and suicidal behavior disorder (SBD) in DSM-5.

In the analysis of self-harm groups based on DSM-5 criteria, adolescents with SBD only had a significantly lower proportion of females than the other two groups similar to a previous study on Korean adolescents [35]. In the current study, the prevalence rate that met the diagnostic criteria for NSSI-D and SBD were 32.8% for NSSI-D and 33.5% for SBD; the prevalence was comparable with the study based on DSM-5 criteria [20].

There was a higher proportion of female patients in the self-harm group than the without self-harm group. This is consistent with results showing females had a greater rate of NSSI and that gender differences are more obvious among clinical patients [36]. However, it should be noted that our study included a higher total number of female adolescents. A previous study on the inpatients sample showed 65% to 71% of the adolescents were female and is close to the gender ratio in our study, which makes sense in the context of clinical reality [36-39].

With respect to suicidal ideas, there was a significant number of adolescents with self-harm who reported suicidal ideation than those without self-harm. In this study, broader definition of self-harm was used, and self-harm group included patients with SA. Notably, self-harm group in our sample showed more suicidal ideation than previous studies with NSSI [40]. In this study, even in the NSSI-D only group, in which suicidal behavior was not observed, the percentage of suicidal ideation was 65.7%, indicating a high rate. Therefore, a sample of our study of patients with self-harm including NSSI-D only group appeared to have high rate of suicidal ideation. In logistic regression, suicidal ideation was significantly associated with self-harm. Although NSSI is not associated with conscious suicidal intent, it is the strong predictor of suicidal ideation and suicidal attempt [41,42].

As in a previous study performed in the United States [1], the rate of physical or sexual abuse was also high in the self-harm group in this study. In addition, sexual, physical, emotional abuse, and emotional neglect, have been associated with self-harm in studies conducted in several other countries [43,44]. Thus, regardless of race or geographical location, childhood abuse appears to increase the risk of self-harm. Verbal abuse was considered as an abuse in this study, which is a concept that has been considered as an emotional abuse in previous studies. Therefore, since this study did not divide and compare the abuse types, we did not find which types of abuse have a greater effect on self-harm behavior. However, in future, if we employ objective methods according to each abuse, we will have a better understanding of the link between abuse and self-harm.

Addition to verbal, physical, or sexual abuse, patients with self-harm reported significantly more parental conflict and parent-child relational problems than patients without self-harm. These results are in line with those of a previous study that found that stressful life events were associated with self-harm [45]. Stressful life events include parental separation, divorce, and witnessing domestic violence, in addition to abuse and neglect [46,47], and it seems that adolescents are more exposed to these childhood adversities when they have parent-child relational problems or parental conflict. Bullying was more common in the self-harm group than in the control group, but there was no statistically significant difference. However, given that prior studies were done on a wide scale [6,7], it is probable that the difference did not occur owing to the limited number of participants in this study. Among the negative life events related to self-harm, the parent-child relationship problem was significantly high only in adolescents with both NSSI-D and SBD. Our findings suggest that the parent-child relationship is an important risk factor for suicide in adolescents with NSSI-D only. In a previous research study, individuals with NSSI only reported fewer negative events than those with NSSI and SA [48]. Emotional abuse and neglect in childhood have been linked to suicidal ideation and attempts in adolescents, especially severe SAs [49]. In the neurobiological developmental model of NSSI, adolescents with NSSI showed altered hypothalamic-pituitary axis and autonomic nervous system function, contributing to stress vulnerability [50]. In this context, it can be assumed that traumatic and persistent childhood adversity reduces the ability to cope with stress and appears as a more severe form of behavior on a continuum between NSSI and SA. Future research is needed on whether stress vulnerability differs according to the type of childhood adversity and biological factors that mediate the degree of serious self-harm.

There were no significant differences in psychological assessment in the analysis of the self-harm group divided into three subgroups. Regardless of suicidal intentions, it means that the difference in clinical scale is not significant in groups with self-harm. These results are in line with those of a previous study examining adolescents with NSSI and SAs in which there were no significant differences in clinical scores representing psychological symptoms [35].

With respect to psychiatric diagnosis, patients with self-harm were distributed a wide spectrum of diagnoses. The proportion of the disease group is close to that of a recent study with a Korean adolescent clinical sample, where 61.5% of the adolescent with NSSI were diagnosed with depressive disorder and 34.6% were diagnosed with bipolar disorder [21]. In the analysis that divided the self-harm group into three groups, the NSSI-D only and SBD only groups showed a significantly higher proportion of depressive disorder than both NSSI-D and SBD groups. In addition, the proportion of bipolar disorder was higher in both NSSI-D and SBD than in the other two groups, even though there was no statistically significant difference. For depression and bipolar disorder, the group with NSSI-D only and the group with SBD only showed similar disease distribution. This suggests that SAs in patients with NSSI have different characteristics from those without NSSI in terms of psychiatric diagnosis. In addition, the NSSI-D group with SBD showed different diagnostic profiles from the NSSI-D group without SBD. This seems to be an important implication for potential suicidal behavior in adolescents with NSSI-D.

With respect to functionality, there were no significant differences in the functionality of self-harm. Affect regulation was the most common reason for self-harm in both the NSSI-D and SBD and NSSI-D only groups, which is consistent with previous studies [41,51]. The urge to escape from an intolerable state of mind is a prominent motivation for self-harm, as supported by empirical [52] and theoretical research [53]. In consistence with this idea, previous research found that NSSI for affect regulation was significantly related to a history of SAs [51]. Our result showed that the motivation for affect regulation was not significantly different between the NSSI-D only group and both NSSI-D and SBD groups.

Patients with both NSSI-D and SBD and patients with NSSI-D only are more likely to use cutting for self-harm than patients with SBD only. Patients with both NSSI-D and SBD and patients with SBD were more likely to use self-poisoning for self-harm than patients with NSSI-D [54]. Jumping and hanging rates were significantly higher in both the NSSI-D and SBD groups and SBD only group than NSSI-D only group. These findings imply that adolescents with NSSI should be more conscious of the dangers of suicide behavior if they have a history of self-harm through poisoning, hanging, or jumping.

There were several limitations to our analyses. First, as the subjects were limited to one university hospital, variables of referral hospital may have influenced the interpretation of the results. Therefore, the sample size in this study was not an accurate representation of the clinical group or general adolescent population. Second, due to the limitations of retrospective chart review, the possibility that the variables included in the analysis were omitted and underestimated in the recording process cannot be ruled out. Third, since it is a cross-sectional study evaluated based on the time of hospitalization, the factors related to self-harm in the results cannot explain the casual relationship. Fourth, factors related to self-harm, such as parentchild relational problem, were classified according to presence or absence, and the qualitative evaluation was insufficient in this study. Fifth, when comparing the presence or absence of self-harm, self-poisoning was included; however, there was a limitation in that self-poisoning was excluded when in the comparison between the three self-harm groups because of the diagnostic criteria of NSSI.

Despite these limitations, this study is meaningful in that it was able to analyze self-harm-related factors and diagnoses for clinical adolescent groups with various diseases and identify results consistent with previous studies, which were limited to specific patient groups. In addition, we employed a broad self-harm definition to reduce misunderstanding in self-harm research. Meanwhile, in the future, further studies on the prevalence of NSSI and SBD in a wide range of conditions for further study using the DSM-5 criteria are required.

In conclusion, this study analyzed the psychosocial and clinical characteristics of hospitalized adolescents with various psychiatric diseases by dividing them into self-harm and non-self-harm groups. This study showed that female gender, suicidal idea, adverse experience associated with self-harm, and psychiatric diagnosis are associated with self-harm. The most common diagnosis in the self-harm group was depression, followed by bipolar disorder. Also, our results demonstrated that difficulties in relationships with parents and parental conflict were related to selfharm. Furthermore, when the self-harm group was divided into three categorical groups, each of the three groups exhibited different diagnostic profiles; therefore, future research should further develop and confirm initial findings by considering these three categorical groups.