It's called food allergy bullying, and it's a new trend that is endangering children with allergies.

Researchers estimate that 5.9 million children under age 18 in the United States have a food allergy. That's 1 in 13 children, or roughly two in every classroom. And more than 40 percent of them have experienced a severe or life-threatening reaction. That's why food allergy bullying is so dangerous.

It is happening in schools all over the country. In a recent case near Pittsburgh, three teenagers were charged with intentionally exposing a classmate to pineapple despite knowing she had an allergy to the fruit. The student had to receive immediate treatment. And a 7-year-old Utah boy came home in tears after his classmates threatened to make him eat peanuts -- knowing he was severely allergic. Others report having food thrown at them.

These incidents are not rare. A recent study by Mount Sinai Medical Center found that nearly a third of kids with a food allergy have experienced similar bullying.

"This is a very frightening trend that we've seen here in our local school districts as well," says Dr. Sai Nimmagadda, a pediatric allergist at Advocate Children's Hospital. "These bullies need to know that they could actually cause serious harm by forcing another child to eat something they are allergic to. An allergic reaction can threaten a child's life."

Parents, teachers and school administrators need to be aware that the threatening is happening among kids, according to Nimmagadda.

"The school environment should be a place of safety and no child should experience any form of bullying," he said. "The emotional aspects of food bullying can lead to serious psychological effects, if not discovered and treated early on."

There are also other serious consequences. The teens in Pittsburgh are now facing felony criminal charges.

"I'd suggest all parents have a conversation about this at the dinner table," Nimmagadda said. "What seems like harmless fun can turn dangerous quickly. We just need to make sure children and teens understand the repercussions before someone gets seriously hurt."

• Children's health is a continuing series. This week's article is courtesy of Advocate Children's Hospital. For more information, visit www.advocate