People of all ages, genders, sexualities, ethnicities, and social classes self-injure, though there are factors that may increase the likelihood that an individual will self-injure.

Age

Current research suggests that self-injury most commonly begins between ages 12 and 15 (Plener et al., 2015), with a second onset peak in early adulthood, around age 20 (Ghandi et al., 2018). Some people first start to self-injure before the age of 12 and some first self-injure much later in life. An age of onset before 12 is associated with more severe self-injury over a longer period of time (Muehlenkamp et al., 2019). Typically rates of self-injury increase through early-mid adolescence and decline in later adolescence.

​Sex, gender, and sexuality

A 2015 meta-analysis of 116 studies showed that girls and women are slightly more likely to self-injure than boys and men, with this gender difference particularly evident in clinical samples. Self-injury is also more common among individuals identifying within the LGBTQIA+ community, with rates 2-3 times that of heterosexual/cisgender individuals (Liu et al., 2019).

Culture and race

A majority of research to date has focussed on samples comprising mostly Caucasian individuals from Western societies. This has lead to a significant gap in our understanding of NSSI among individuals in underrepresented cultural and racial groups. Current knowledge suggests that self-injury is present across cultures and races. A review by Gholamrezaei et al. (2015) showed there may be differences in age of onset and function, but the differences are complicated by social and economic factors, often brought about by racism. 

Psychological profile

A meta-analysis (Fox et al., 2015) found that risk factors for self-injury include depression, hopelessness, abuse, personality and eating disorders, and impulsivity. People who engage in self-injury report being more sensitive to interpersonal stress or conflict, and experiencing greater difficulty expressing and regulating their emotions. That being said, most people who engage in self-injury do not have a mental illness.

Trauma and hardship

Experiences of trauma can leave lasting psychological damage resulting in instrusive thoughts, flashbacks, painful emotional states, and dissociation. Self-injury may be used by individuals facing these experineces, as it can be an effective strategy for escaping unwanted experiences and ending dissociation (Smith et al., 2014). Whilst people who have experienced trauma are more likely to engage in self-injury (Liu et al., 2018), it is a myth that all people who self-injure have experienced childhood trauma. Poverty is an additional risk factor for self-injury, with individuals from impoverished backgrounds more likely to self-injure than individuals whose socioeconomic needs were met (Liu, 2021).

Why People Self-Injure

Self-injury can be difficult to understand, as it appears to go against humans' innate desire to avoid harm. However, the reasons someone might injure themselves on purpose are often similar to the reasons people engage in other behaviours.

Individuals who have self-injured often report more than one reason for their self-injury, and their reasons may change over time. The functions of self-injury can be classified into two broad categories: intrapersonal and interpersonal. Self-injury for intrapersonal reasons is more common than for interpersonal reasons (Taylor et al., 2018).

Intrapersonal Functions

Intrapersonal reasons have to do with an individual's internal state, including thoughts and emotions. There are three main intrapersonal functions:

Emotion regulation. The most commonly reported reason to engage in self-injury is to manage emotional experiences. This includes escaping an unwanted emotions or inducing a desired emotion. Typically, these emotions are "negative", such as anger, frustration, sadness, and loneliness, but "positive" emotions such as excitement or pride have also been reported.

Thought regulation. This is closely linked to emotion regulation, as our thoughts and emotions are connected. Individuals may use self-injury to control or quieten unwanted thoughts, such as self-criticism or suicidal ideation.

Self-punishment. While self-punishment appears to serve an emotion regulation purpose, self-injury for this reason is usually tied to feelings or shame or thoughts about oneself being "flawed" or "bad".

Interpersonal Functions

Interpersonal functions have to do with an individual's connection with others, and include three main reasons:

Communicating distress. Sometimes individuals may not know how to explain their distress to others and use self-injury as a way to communicate their feelings. 

Social influence. There may be several motivations underlying self-injury as a way to influence others. An individual may engage in self-injury to keep people away from them, to demonstrate their belonging to a social group, to elicit care, or to encourage a change in behaviour.

Punishment. Sometimes a person may engage in self-injury as a way to punish another person for something they have or have not done. In these instances, the self-injury is typically communicating distress and serving an emotion regulation function as well.

References

• Fox, K. R., Franklin, J. C., Ribeiro, J. D., Kleiman, E. M., Bentley, K. H., & Nock, M. K. (2015). Meta-analysis of risk factors for nonsuicidal self-injury. Clinical Psychology Review, 42, 156-167. https://doi.org/10.1016/j.cpr.2015.09.002

• Gandhi, A., Luyckx, K., Baetens, I., Kiekens, G., Sleuwaegen, E., Berens, A., Maitra, S., & Claes, L. (2018). Age of onset of non-suicidal self-injury in Dutch-speaking adolescents and emerging adults: An event history analysis of pooled data. Comprehensive Psychiatry, 80, 170-178. https://doi.org/10.1016/j.comppsych.2017.10.007

• Gholamrezaei, M., De Stefano, J., & Heath, N. (2015). Nonsuicidal self-injury across cultures and ethnic and racial minorities: A review. International Journal of Psychology, 52, 316-326. https://doi.org/10.1002/ijop.12230

• Liu, R. R. (2021). The epidemiology of non-suicidal self-injury: Lifetime prevalence, sociodemographic and clinical correlates, and treatment use in a nationally representative sample of adults in England. Psychological Medicine, 53, 274-282. https://doi.org/10.1017/S003329172100146X

• Liu, R. T., Scopelliti, K. M., Pittman, S. K., & Zamora, A. S. (2018). Childhood maltreatment and non-suicidal self-injury: A systematic review and meta-analysis. The Lancet - Psychiatry, 5, 51-64. https://doi.org/10.1016/S2215-0366(17)30469-8

• Liu, R. T., Sheehan, A. E., Walsh, R. F. L., Sanzari, C. M., Cheek, S. M., & Hernandez, E. M. (2019). Prevalence and correlates of non-suicidal self-injury among lesbian, gay, bisexual, and transgender individuals: A systematic review and meta-analysis. Clinical Psychology Review, 74, Article 101783. https://doi.org/10.1016/j.cpr.2019.101783

• Muehlenkamp, J. J., Xhunga, N., & Brausch, A. M. (2019). Self-injury age of onset: A risk factor for NSSI severity and suicidal behavior. Archives of Suicide Research, 23, 551-563. https://doi.org/10.1080/13811118.2018.1486252

• Plener, P. L., Schumachers, T. S., Munz, L., & Groschwitz, R. C. (2015). The longitudinal course of non-suicidal self-injury and deliberate self-harm: A systematic review of the literature. Borderline Personality Disorder and Emotion Dysregulation, 2, Article 2. https://doi.org/10.1186%2Fs40479-014-0024-3

• Smith, N. B., Kouros, C. D., & Meuret, A. E. (2014). The role of trauma symptoms in nonsuicidal self-injury. Trauma, Violence, and Abuse, 15, 41-56. https://doi.org/10.1177/1524838013496332

• Taylor, P. J., Jomar, K., Dhingra, K., Forrester, R., Shahmalak, U., & Dickson, J. M. (2018). A meta-analysis of the prevalence of different functions of non-suicidal self-injury. Journal of Affective Disorders, 227, 759-769. https://doi.org/10.1016/j.jad.2017.11.073