Self-Injury Hurts! When it comes to pain, I am a wimp. If I accidentally hit my thumb with a hammer I'm ready to call an ambulance. Like many, I had a hard time understanding how those who self-injure report experiencing little or no pain when hurting themselves. It could be that there's a huge conspiracy among self-injurers to state that the act of hurting themselves is not painful in an attempt to recruit more self-injurers. But it seems more likely that there are psychological and physiological processes that help to mask the pain associated with the physical injury.
Self-injury is cyclic in nature with factors preceding the actual act of physical injury and factors following the behavior. Dissociation is one of the factors that comes into play immediately prior to the act of self-injury. Everyone dissociates to some degree. At a benign level, dissociation may be described as "zoning out" and may result in driving past the freeway ramp on which you intended to exit. At the extreme end of the dissociative spectrum is dissociative identity disorder, a psychological phenomenon in which an individual develops, typically as the result of chronic, severe trauma, two or more distinct personalities. When people self-injure they are typically in a dissociated state, allowing them to feel little or no pain while they injure themselves.
Physiologically, endorphins are released when we are injured or stressed. Endorphins are neurotransmitters that act similarly to morphine and reduce the amount of pain we experience when we are hurt. Joggers often report experiencing a "runners high" when reaching a physically stressful period. This "high" is the physiological reaction to the release of endorphins - the masking of pain by a substance that mimics morphine. When people self-injure, the same process takes place. Endorphins are released which limit or block the amount of physical pain that's experienced. Sometimes people who intentionally hurt themselves will even say that they felt a "rush" or "high" from the act. Given the role of endorphins, this makes perfect sense.
These two dynamics, dissociation and the release of endorphins, serve to mask the physical pain that would seem to accompany self-injury. Regardless of whether the injury we sustain is accidental or intentional, our body knows how to protect itself.