Hello. I believe I can be of help to you with this issue.
Most people who self-injure do so because it helps them regulate highly aversive emotions. That is, people who cut or purposely burn themselves have not learned healthier ways to cope with terribly painful or aversive emotions. The causes of these emotional problems are being placed in situations in which they feel extreme emotional distress and perceive that they are utterly helpless to change the awful life situation or escape it. Such situations are for example,major emotional or personal losses, living in a violent or intensely contentious family circumstance; being physically or sexually abused as a child or adolescent, or any other inescapable, "helpless" situation that involves intense upset, stress
Research suggests that self-injurers are not intent on committing suicide; self-injury distracts them from feeling badly; it can help change their feeling state if they focus on the cut and blood flow; some report that cutting themselves relieves their feelings of emotional numbness
. So there are many purposes served by self-injury which may vary a bit from person to person; but emotion regulation and as a way to indirectly express hurt feelings is the best general explanation. It is true that a few self-injurers inflict plain on themselves to escape or avoid work (e.g., obtain disability payments), or to obtain the care and attention of employers, health care workers, etc. (this is called Munchausen's syndrome when it becomes extreme). Teens will sometimes self-injure to draw attention to their distress, because they don't feel like they can verbally request it.
If you wish to try to be helpful, you can explain that you suspect your son's self-injury is certainly tied to the disappointments he has experienced in his social world. Since it is very hard to deal with feelings of hurt and anger, you are aware that he may be harming himself to regulate stress and difficult emotions, and perhaps ask for help and understanding. Let me pause here and prompt you to respond and react to what I've said so far.