It's Turning the Pain Inside Out

People who self abuse are usually turning emotional pain into physical pain. For most it is a way of letting the pain out. When they feel alone, helpless, hurt, or angry the only way to sooth their pain is to use self-injurious behavior.
Letting out emotions with pain is both symbolic and physically real. After one cuts them self, the person’s body releases endorphins, chemicals from the brain that help the body cope with pain. Thus creating a temporary high which may or may not cause the person to become addicted to. In turn they may have to hurt themselves more severely the next time in order to get the same calming effect.