But there are very few dedicated research centers for self-harm, and even fewer clinics specializing in treatment. When youngsters who injure themselves seek help, they are often met with alarm, misunderstanding and overreaction. The apparent epidemic levels of the behavior have exposed a structural weakness of psychiatric care: Because self-injury is considered a “symptom,” and not a stand-alone diagnosis like depression, the testing of treatments has been haphazard and therapists have little evidence to draw on.

In the past few years, psychiatric researchers have begun to knit together the motives, underlying biology and social triggers of self-harm. The story thus far gives parents — tens of million worldwide — some insight into what is at work when they see a child with scars or burns. And it allows for the evaluation of tailored treatments: In one newly published trial, researchers in New York found that self-injury can be reduced with a specialized form of talk therapy that was invented to treat what’s known as borderline personality disorder.

“It used to be that this kind of behavior was confined to the very severely impaired, people with histories of sexual abuse, with major body alienation,” said Barent Walsh, a psychologist who was one of the first therapists to focus on treating self-injury, at The Bridge program in Marlborough, Mass., now a part of Open Sky Community Services. “Then, suddenly, it morphed into the general population, to the point where it was affecting successful kids with money. That’s when the research funding started to flow, and we’ve gotten a better handle on what’s happening.”

Joan was 13 when the cutting began. Now 16, she had greatly curtailed this routine in the past few months, she said: “But I still do it, like, every week or so.”

The most common misperception about self-injury is that it is a suicide attempt: A parent walks in on an adolescent cutting herself or himself, and the sight of blood is blinding. “A lot of people think that, but in reality, you cut for different reasons,” said Blue, 16, another high school student in the New York area, who asked that her last name be omitted. “Like, it’s the only way you know to deal with intense insecurities, or anger at yourself. Or you’re so numb as a result of depression, you can’t feel anything — and this is one thing you can feel.”