Most of the time, researchers found, the injuries were not life-threatening, and included acts such as cutting, piercing and burning.
But, while the total numbers remained relatively low, experts said the increase in self-injuries is concerning.
Because acts like cutting or burning can be easily hidden, ER records would capture only a small percentage of all kids who harm themselves, said Gretchen Cutler, the study's lead researcher from Children's Hospitals and Clinics of Minnesota. "Kids who self-harm are at higher-than-average risk of eventually attempting suicide," she said.
The study included almost 287,000 10- to 18-year-olds who were treated in an ER between 2009 and 2012.
Overall, 1.3 percent of those kids, nearly 3,700 were diagnosed with a self-inflicted injury. The most common cause was cutting, followed by firearm injuries. Burns, intentional falls, suffocation and poisoning were among the other ways kids hurt themselves.
Just over 4 percent died from their injuries making kids who self-harm 13 times more likely to die in the ER than kids treated for other reasons. The firearm injuries actually declined, from 27 percent of all self-inflicted injuries, to 22 percent.
Cutting injuries increased over time, and it was particularly common among girls accounting for almost half of their self-inflicted injuries.
Why do some kids hurt themselves, without any suicidal intent? "Most often, they're looking for a way to manage emotional turmoil," said Angelosante a child psychologist at NYU Langone Medical Center. "They might be sad, or anxious, or angry. And something about the physical pain helps with the emotional stress."
There can be other reasons, too. Some kids do it because they have a sense of being "numb," and want to feel something, Angelosante said. For others, self-harm is their way of revealing how emotionally overwhelmed they are.
For parents, Angelosante said, it's important to be aware that kids sometimes try self-harm as a way to deal with stress. She pointed to some red flags: Is your child suddenly covering up his skin more than usual? Is she quickly going through bandages or razors?
If a child has a self-inflicted injury, the first step is to have a doctor check it out.
Kids who habitually self-harm probably need professional help to deal with the underlying issues.