Adolescent suicide is a major public health problem among adolescents in South Korea [1]. Self-harm has been recognized as a key predictor of suicidal behavior [2]. Self-harm refers to a deliberate behavior by an individual to cause harm to themselves that results in a nonfatal outcome [2]. Although the prevalence of adolescent self-harm worldwide varies due to differences in definitions of the phenomenon between and within countries, its overall lifetime prevalence among adolescents is estimated to be 10%, and female adolescents are more likely to report self-harm than male adolescents [2,3].

Adverse childhood experiences (ACEs) refer to early-life exposure to violence, physical and sexual abuse, neglect, and a household environment in which a household member had struggled with substance abuse, mental disorders, parental separation, or imprisonment [4]. Studies have shown that ACEs could lead to negative health consequences in adulthood, such as alcoholism, substance use disorder, depression, and suicidal ideation [4,5]. Research on ACEs has also reported a strong graded relationship between ACEs and negative health outcomes, such that the more ACEs individuals are exposed to, the greater the risk of physical and mental health problems in later life [4]. Unfortunately, few studies have examined the proximal effects of ACEs on behavioral problems during adolescence [6].

Although a strong relationship exists between exposure to ACEs and a range of behavioral problems, variations in the prevalence of ACE exposure and in behavioral problems by subgroup characteristics (e.g., race and ethnicity, gender, or maternal education) have been reported [6]. Studies of selfharm have consistently shown that the rates of self-harm are higher among female adolescents than they are among male adolescents [2]. Yet, there is not enough evidence to indicate whether one gender is more exposed to ACEs than the other or whether one gender is more susceptible to the impact of ACEs than the other [7]. Scant research has been dedicated to self-harm among children, and little is known about gender differences in childhood behavioral problems among those who have been exposed to ACEs.

Developmental research indicates that exposure to maltreatment during childhood may create a risk of insecure child-caregiver relationships during adolescence and adulthood [8]. The literature further suggests that children who have an insecure attachment to their caregivers may have difficulties regulating their intense emotions; this presents as externalizing behavioral problems such as self-harm, suicidality, substance abuse, and aggression [9,10].

The link between exposure to ACEs and an array of behavioral problems among children and adults has been well established [4,11]. However, most studies have been conducted in Western societies. Few studies have examined the impact of ACEs on Asian adolescents. Examining the influence of ACEs among Asian populations is critically important because different cultural contexts may affect patterns of ACE occurrence and the extent to which individuals are susceptible to adversity [12]. For example, some researchers have suggested that the prevalence of child physical abuse in Asian countries, where strict parenting is espoused, is significantly higher than in Western countries [13].

To address these issues, we investigated the associations between lifetime exposure to ACEs and a lifetime history of self-harm among a sample of Korean children and adolescents in K-12 schools. We also explored the specific and cumulative effects of ACEs on self-harm among male and female adolescents. Based on the literature, we predicted that more ACEs would be positively associated with self-harm history among Korean children and adolescents. However, we could not predict gender differences in the association of ACEs with adolescents' history of self-harm because the findings in the literature are inconsistent.

Data on 171 Korean children and adolescents were analyzed. The mean age was 12.3±3.4 years old (Table 1). More than half of the sample were male (54.4%) and attended middle school or above (51.5%). Most of them lived in an urban area (61.4%). Of that group, 36.3% presented a history of self-harm (Table 1). Students with a history of self-harm were older (14.0±3.0 vs. 11.4±3.2 years old). Female students reported a history of self-harm more frequently than their male counterparts (50.0 vs. 24.7%). High school students (61.8%) exhibited a higher proportion of reported self-harm than middle (46.3%) and elementary school students (19.3%).

Table 2 presents a frequency comparison of ACEs among children and adolescents using their histories of self-harm. The data show that 62.0% had at least one ACE; the most frequently reported ACEs were undifferentiated neglect (28.7%), parental divorce (26.3%), and emotional abuse (14.6%). Children and adolescents with a history of self-harm experienced more physical abuse (57.1% vs. 42.9%; x²=4.52, p=.034) and emotional abuse (56.0% vs. 44.0%; x²=4.94, p=.026). The cumulative frequency of ACEs was found to be statistically significantly different between the two groups of students (x²=8.15, p=.017). Table 3 shows a frequency comparison of covariates by history of self-harm. The most frequently reported covariates were school absenteeism (36.3%), violent behavior (33.3%), and anxiety (32.7%). Children and adolescents with a history of self-harm were more likely to present with a history of depression (55.6% vs. 44.4%, x²=12.72, p<.001).

Multiple logistic regression analyses revealed three predictors of a history of self-harm among Korean children and adolescents (Table 4). After adjusting for demographic data and covariates, children and adolescents who (a) attended high school (adjusted odds ratio [aOR]=4.97; 95% confidence interval [CI]=1.94-12.76), (b) had a history of two or more ACEs (aOR=3.27; 95% CI=1.43-7.47), and (c) had depression (aOR=3.06; 95% CI=1.32-7.10) were three to five times more likely to have a history of self-harm compared to those who did not.

This study explored the association between ACEs and self-harm among Korean children and adolescents. We found that 36.3% of the sample reported a history of self-harm, which substantially exceeded the rates of self-harm reported by adolescents in previous studies [20]. In their population-based cohort study, Moran and colleagues investigated the natural history of self-harm among adolescents aged 14 to 15 until the age of 29 years and found that 8.3% of youth reported selfharm during their adolescent years. They also reported that the prevalence of self-harm was closely related to distribution of age and gender. They reported that the prevalence of self-harm was highest during late adolescence and decreased in young adulthood (2.6%). The gender-specific prevalence of self-harm was 10% among boys and 6% among girls. Furthermore, research [21] that demonstrated the potential of the COVID-19 pandemic to increase rates of self-harm or presentation of suicidal ideation in emergency departments may partially explain these differences because our study was conducted during the COVID-19 period.

We also found that self-harm was more commonly reported by female adolescents than by male adolescents. This is consistent with the findings of general population studies [20,21]. However, there were no gender differences in the association of ACEs with self-harm when adjusting for covariates in multivariate logistic regression. Our results were not aligned with prior findings that reported gender differences in the effects of specific childhood traumatic experiences on various internalizing or externalizing symptoms [22]. There may be specific cultural factors that offset the gender-based differential symptomatology associated with childhood exposure to adversity.

In our study, the proportion of students who disclosed experiencing any form of ACEs closely resembled previously reported figures [12]. Nevertheless, the potential for underreporting must be acknowledged, given that students frequently met with their counselors alongside their parents, and neither the counselors nor the medical professionals utilized standardized tools to evaluate ACEs. It is important to note that the assessment of ACEs is infrequently conducted within clinical and school settings in Korea [23]. Our results revealed a graded relationship between cumulative lifetime exposure to adversity and the incidence of self-harm: 49.1% of adolescents with two or more ACEs reported a history of self-harm, while 29.8% of adolescents with 0-1 ACEs reported a history of self-harm. This finding is consistent with a previous study that examined the impact of ACEs on suicide attempts among adolescents [24]. This shows that the number of ACEs may be a risk factor for self-harm among children and adolescents.

Furthermore, Marie-Mitchell and O'Connor [19] raised the possibility of using preexisting records to assess ACEs among children and adolescents. They obtained the self-reported data of parents and conducted a medical record review of children to identify suspected maltreatment, domestic violence, substance use, mental illness, criminal behavior, and single parenting. The researchers did not present the results of psychometric evaluation. However, they did show that there were statistically significant differences in behavioral problems, developmental delay, and injury and obesity between the lowand high-risk groups and indicated that medical record review was a feasible method for screening purposes.

Finally, we noticed that students with a history of depression were 3 times more likely to present self-harm than those without a history. This finding is consistent with previous research [20] finding that youth with a history of depression or anxiety were 3.8 times more likely to present self-harm. In our statistical model, depression was an independent contributor to self-harm. This finding is significant because depression may have worsened as a result of the COVID-19 pandemic, potentially accelerating self-harm. In their natural experimental study, Mansfield et al. compared the mental health of adolescents before and during the COVID-19 pandemic using two randomized controlled trials [25]. They reported that the COVID-19 group presented more depressive symptoms and estimated that 6% of students would not have presented high depressive symptoms if the pandemic had not occurred. The researchers also noticed that female students were more vulnerable to the negative impact of the pandemic on their mental health than male students. Woo and their colleagues conducted a comprehensive cross-sectional survey across the nation [26]. Their findings also indicated an elevation in feelings of sadness and instances of suicidality among Korean adolescents during the COVID-19 pandemic period.

This study has several limitations. First, since the data were retrieved from consulting records for counseling purposes, not research, misclassification bias could have been an issue. Marie-Mitchell and O'Connor [19] raised the possibility of using preexisting records to assess ACEs among children and adolescents. They obtained the self-reported data of parents and conducted a medical record review of children to identify suspected maltreatment, domestic violence, substance use, mental illness, criminal behavior, and single parenting. The researchers did not present the results of psychometric evaluations. However, they did show that there were statistically significant differences in behavioral problems, developmental delay, and injury and obesity between the low- and highrisk groups and indicated that medical record review was a feasible method for screening purposes. Furthermore, the frequency and intensity of ACEs were not considered in our analysis because no such data were available in the consultation records. These variables may have stronger relationships with the lifetime history of self-harm among adolescents than the lifetime exposure to ACEs. Second, because our results were based on cross-sectional data, causality in the observed associations cannot be inferred. However, we believe that the possibility of reverse causality (i.e., self-harm occur-ring before children are exposed to adversity) may be low. Third, our results are based on a small and somewhat selective sample of referred counseling cases that school counselors deemed to be beyond their expertise. Thus, the generalizability of our findings to other populations is limited. Finally, our sample comprised children and adolescents who were seen by school counselors. We probably underestimated the actual prevalence of self-harm among this population because some students may have gone to other services or never sought help of any kind in the first place.

The study's findings provide compelling evidence that exposure to ACEs can increase vulnerability to self-harm among the K-12 Korean population. The former significantly predicted the odds of the latter. The development and assessment of school-based interventions to screen for ACE exposure and depressive symptoms, coupled with an awareness campaign educating school professionals and students on the impact of ACEs, should be a priority to prevent self-harm among children and adolescents. Further research is needed to better understand subtypes of students who self-harm and the factors associated with different types of self-harm.

Our findings have several implications for preventing selfharm. The high number of children and adolescents with a history of ACEs in this study indicates the need to implement a screening program that can identify students at risk of selfharm. This is critical because only a small proportion of adolescents who engage in self-harm seek help, and most youth go unnoticed and unreported. For high-risk individuals, school counselors can be valuable assets because they can provide an initial psychosocial intervention. Training school professionals (e.g., teachers, school counselors, and school nurses) to recognize risk factors (i.e., ACEs) and warning signs of self-harm should be an integral component of prevention efforts. Our finding that being in high school and being treated for depression were predictors of a self-harm history suggests that school-based strategies should include screening youth, especially high school students, for depression.