Cutting is a form of self-injury practiced by those who are in emotional pain or extreme anxiety. Because of the inability to express these feelings, the pain is released by self- injury. Other forms of self-harm include burning, head banging, and hair pulling.
The intent of self-injury is not suicide but a release of overwhelming feelings. As many as 1% of the United States population uses these behaviors as a means to cope with distressing situations or feelings. Research has shown that an act of self injury often brings immediate psychological relief, perhaps through the release of endorphins, which are chemicals in the brain that serve as the body's natural painkillers.
While it's not entirely understood why some people are more prone to self-injurious behaviors, a common factor among those who harm themselves in this way is that they have never learned how to express distasteful or negative feelings appropriately, or that they have learned that it is wrong to have such feelings. Some studies have suggested that a mix up in the way the brain uses the neurotransmitter serotonin may predispose some people to act impulsively and aggressively.
As a parent, it can be scary and even horrifying to discover that a child is cutting herself. But it's important to remember that this behavior is not suicidal but a maladaptive coping mechanism. And it's not meant to anger or frustrate parents. Staying calm and avoiding shaming the child further (who generally feels embarrassed and ashamed about this behavior already) is best.
A psychological evaluation and subsequent treatment can help to work on problems and issues underlying self-injurious behaviors. The goal of therapy is to help the child to learn and start to use new coping mechanisms for dealing with emotional pain. As a parent, you can help by allowing your child to express negative feelings - without fear of reprisal. You can also be a good role model for a child by dealing with stressful or difficult situations in a healthy way.