Health care providers and educators find few behaviors more alarming than self-injurious behavior (SIB).  SIB is commonly defined as deliberate infliction of physical injury to one’s body without intent to die.  While there may be no intent to die, it is precisely the potential lethality of this behavior that creates alarm.  As many as sixty percent of individuals who engage in nonsuicidal SIB also engage in suicidal behavior.  Further alarm stems from the association between SIB and other serious emotional or behavioral problems (e.g., obsessive-compulsive disorder, borderline personality disorder, psychosis, eating disorder).    
People who engage in SIB are a largely heterogeneous group.  However, based on similar patterns, four major categories of SIB can be designated.  (a) Stereotypic SIB involves repetitive, monotonous, driven acts that seem to be devoid of thought, affect, or meaning.  Common behaviors include head banging, self-hitting, or self-biting.  This type of SIB is commonly associated with mental retardation, autism, or some types of congenital disorders (e.g., Lesch-Nyhan, Prader-Willi, or Cornelia de Lange Syndromes).  (b) Major SIB involves isolated acts of severe and often life threatening self-injury.  The acts can be impulsive or planned and typically occur in the context of psychosis or intoxication.  This type of SIB most frequently includes castration, eye enucleation, and rarely, limb amputation.  (c) Compulsive SIB refers to repetitive and often ritualized behaviors that occur multiple times a day.  These behaviors seem to be obsessive-compulsive in nature in that they are frequently in response to an irresistible urge and result in gratification or relief.  The most common forms of compulsive SIB include trichotillomania (hair pulling), onychophagia (nail biting), and skin picking (neurotic excoriation).  (d) Impulsive SIB includes spontaneous and often symbolic acts that are most typically skin cutting, skin burning, or self-hitting.  These acts often start out as isolated incidents but can become habitual.  This type of SIB is frequently associated with borderline personality disorder, eating disorders, posttraumatic stress disorder, or some form of trauma or abuse.  The remainder of this paper will focus on impulsive SIB.
 Several factors help make sense of this seemingly baffling behavior.  (a) Affect Regulation: Many people who engage in SIB react abnormally to negative feelings.  Their level of arousal goes up much more quickly, peaks at a higher level, and takes more time to settle.  In theory, these people have learned to reduce their negative emotions through SIB.  One-half to three-fourths of SIB patients report anesthesia or relief during the SIB.  On a biological level, the anesthesia might be explained by an addiction hypothesis.  This hypothesis suggests that the endogenous opioid system has been chronically overstimulated for the purpose of alleviating negative feelings.  The individual develops a tolerance to the influx of endogenous opioids, cyclically suffers a withdrawal reaction, and is driven to release more endogenous opioids through SIB. (b) Dissociation: For some people, stress leads them to disconnect from reality or dissociate.  The pain associated with SIB may help them to break through their detachment, reconnect with reality, and feel again.  Many people who engage in SIB report that the behavior helps them feel or that the pain.