Non-Suicidal Self-Injury (NSSI) refers to the behavior that intentionally and repeatedly hurts one's own body, although there is no intention to attempt suicide [1]. This contrasts with the basic behavior of humans seeking pleasure and avoiding pain. Reported prevalence rates of NSSI varied among studies but the prevalence of NSSI in adults is known to be 4~6% [2]. On the other hand, prevalence rates of NSSI in adolescents were reported to be quite high. In a study of the prevalence of NSSI through the survey of a community sample of 1,862 adolescents in three countries, including European countries and the United States, approximately 24% of the adolescents reported at least one NSSI episode [3]. In addition, according to a study of systematic literature review of the prevalence of NSSI in adolescents in schools and local communities, 18% of adolescents reported engaging in NSSI [4]. These study results show that NSSI in adolescents has recently been widespread even in cases other than clinical situations such as mental disorders in Western countries.

In general, NSSI begins in early adolescence of the ages between 12 and 14 years [5], but because it is a behavior that injures one's own body in secret, it is typically not easily detected by the family or in the school until the problem becomes serious, so it is necessary to pay attention to the risk of NSSI among middle school students who are in early adolescence. The most common type of self-injurious behavior is cutting the skin with a knife, and other major types of NSSI include burning, scratching, hitting the areas of the body, and hindering wound treatment. In the case of adolescents, 80% of those reporting engaging in NSSI are reported to exhibit the behavior of cutting or stabbing the skin with a sharp object [6], so although NSSI does not indicate suicidal intention, it is likely to cause physical damage. In addition, NSSI is a high-risk behavior among adolescents' problem behaviors since it can easily lead to suicidal ideation and is likely to lead to death [7] and it can cause psychological distress to the friends and family members around self-injuring adolescents.

NSSI is known as the behavior caused by reciprocal influences of various factors [1]. Looking at an explanation of NSSI from the perspective of learning theory [8], the motivations for NSSI are explained in terms of the positive reinforcement as a behavior to attract others' attention and the negative reinforcement of using NSSI as a coping mechanism to alleviate emotional distress or discomfort. In other words, concerning the most common motivation for NSSI in adolescents, it is said that individuals engage in NSSI in order to fill the emotional holes that cannot be easily healed because of past psychological trauma or abuse experiences such as separation from parents, emotional abuse, and sexual abuse in their childhood and draw the attention of others [9, 10], or NSSI functions as a means of feeling regulation which temporarily alleviates the negative emotions such as anxiety, depression, and stress when such negative emotions cannot be tolerated [3, 6, 9, 11].

Although high prevalence rates of NSSI in adolescents are eliciting high levels of concern and interest around the world, the research on NSSI in Korea has been limited to studies which considered it as the accompanying syndrome in the research of students with disabilities [12] and some adolescents with psychiatric problems [13]. In Korea, there has been no research on the prevalence of NSSI in adolescents in general, and few studies on the risk factors for NSSI have been performed. The reason for this is that NSSI is not easily detected and the conceptual division between NSSI and suicide has been ambiguous for a long time [14]. However, the results of many recent foreign studies have indicated that NSSI is a clinical problem that has different characteristics from suicide and requires a distinct diagnosis for it. Thus, the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders [15] includes the diagnosis of NSSI disorder and mentions it as an area which requires further research.

Therefore, this study aimed to investigate the status of NSSI in Korean adolescents and identify the characteristics of self-harming adolescents in order to provide basic data for understanding the NSSI of adolescents and explore effective ways to conduct an intervention.

This study was conducted to investigate the prevalence of NSSI and the factors related to NSSI in Korean adolescents. Of the adolescents participating in this study, 8.8% reported having experienced NSSI. The subjects of this study were the first to third grade middle school students, and the prevalence rate was similar to 7.5% in the study of Hilt et al. [21], a study of the same age group in North America. However, Hilt et al. [21] is a study of a 12-month prevalence of NSSI, whereas the present study is research on lifetime prevalence, so a direct comparison is difficult to conduct. A study of a systematic review of the lifetime prevalence of NSSI among adolescents in schools and communities in various countries in the western region revealed that on average, about 18% of adolescents had NSSI experience [4]. However, depending on whether the prevalence of NSSI is the lifetime prevalence or the prevalence within 12 months, there are differences in the prevalence of NSSI among studies, and considering that the lifetime prevalence is generally higher, the prevalence of NSSI of 8.8% in middle school students in Korea is relatively low compared with the result of Hilt et al. [21]. However, it is difficult to draw conclusions about the prevalence of NSSI in Korean adolescents because data collection was limited to a local area in this study. Considering the risk of NSSI, it is necessary to identify the prevalence of NSSI by includeing the relevant item in a large-scale survey at the national level such as the online survey of youth health behavior.

In the present study, concerning the characteristics of the adolescents' NSSI, carving letters or pictures on the body was the most frequent self-injurious behavior. However, in a study of Canadian adolescents [6], the rates of behaviors such as cutting the skin such as the wrist (41%) and hitting oneself (33%) were found to be high. In addition, in the study of adolescents with the experience of NSSI in the Netherlands and Belgium [22], the rate of banging or hitting the head was the highest at 12.9%, while in this study, the rate of banging the head was the third highest. Although the sequence was slightly different, among NSSI characteristics, carving a letter or a picture on the body, cutting the wrist with a knife, and banging the head were among the behaviors which showed high rates in the previous studies as well although ranked differently. This may have been influenced by socio-cultural factors, and it is thought that further future research is needed because there is a lack of prior studies to clarify what cultural characteristics cause such behaviors.

In this study, drinking, anxiety, and abusive parenting attitude were the factors that explain NSSI in adolescents. Among them, drinking was found to be the most influential factor of NSSI. This finding is similar to the results of the study which reported that drinking was directly associated with NSSI in female students [12]. Drinking is a predictor of impulsive behaviors among young adolescents [23] and is likely to lead to other dangerous health behaviors [3], which may lead to the possibility of NSSI and suicide. In the United States, smoking and marijuana use were associated with a higher prevalence of NSSI rather than drinking. In the Netherlands, drinking and smoking were not associated with NSSI, but the use of drugs such as marijuana was related to the high prevalence of NSSI. In this regard, according to Giletta et al. [3], NSSI is a social behavior that is not legally recognized, smoking, drinking and using drugs are similarly prohibited for adolescents, and the mechanisms for selecting each are similar. Therefore, the factors affecting NSSI may change depending on whether each of smoking, drinking, and using drugs is a socially acceptable behavior and the purchase of each of them is legally permitted in the nation. However, in Korea, both smoking and drinking are unacceptable behaviors for teenagers, and smoking is subject to stricter social regulation than drinking, which is thought to explain the results different from the interpretation presented by Giletta et al.[3]. Thus, further research is required to understand the interaction between drinking or smoking and NSSI.

In this study, adolescents' experience of abuse by their parents was found to be associated with NSSI, and this finding supports the results of previous studies [24, 25, 26]. If you are exposed to abuse such as blame or disdain by your parents, the risk of NSSI may increase because your selfdisparagement becomes worse and you lack the ability to comfort yourself or control your impulse. According to the self-punishment hypothesis [1], if children who were exposed to abuse by their parents become adults and face stressful situations, they exhibit self-injurious behavior to control and cope with stress or unpleasant emotions, re-experiencing familiar abusive experiences they experienced and learned repeatedly from their parents in the past.

In addition, in this study, anxiety was found to be significantly related to NSSI. This result supports the previous theory of motivations for NSSI which stated that controlling negative emotions is the main function of NSSI [1], and it is consistent with empirical studies which reported that the higher the level of anxiety, the higher the rate of NSSI [3, 6]. However, although previous studies reported that depression was also a variable highly associated with NSSI [3, 6], but it was not a related variable in this study, so further repeated research needs to be conducted in the future.

Other research reported that self-esteem was a factor explaining NSSI in female students [12], but it was excluded in the regression analysis in this study. In this study, although self-esteem was not related, NSSI was found to increase in adolescents with negative emotions and low selfesteem. Thus, in order to prevent NSSI among adolescents, a program including a strategy for strengthening positive attitudes toward oneself and appropriately dealing with negative feelings is considered necessary.

This study has the following limitations. First, there is a possibility that there were recall bias since data were collected by the self-administered questionnaire method. Second, it may have been due to social desirability bias that the prevalence of NSSI was found to be lower in this study than in foreign studies, because NSSI is a socially unacceptable behavior. In addition, since it is a cross-sectional study, this study has a limitation on clearly explaining the causal relationship between variables. Despite these limitations, this study obtained some meaningful results in that this study provided basic data for informing adolescent health care professionals that they should consider NSSI as one of the health risk behaviors of adolescents even in community-based environments by investigating the status of NSSI in early adolescents in Korea and the related factors, and contributed to utilization of the data as the primary data in planning a youth health promotion project.

The purpose of this study was to investigate the prevalence of NSSI in adolescents and to identify the factors influencing NSSI. The prevalence of NSSI in Korean adolescents was found to be 8.8%, and drinking, anxiety and abusive parenting attitude were reported to account for 20% of self-harming behaviors. This study provided basic data for the development of nursing interventions that can reduce NSSI in adolescents through understanding of NSSI experiences of adolescents.

Based on the study results described above, we present the following suggestions.

First, repeated investigations involving more subjects are needed to identify the prevalence rate of NSSI in adolescents by methods such as the online survey on youth health behavior. Second, mental health promotion programs are needed to help to deal with negative emotions such as abusive parenting experiences and anxiety in a positive way, which were considered as risk factors for NSSI in adolescents.