Q. My 18-month-old held his breath until he passed out. It was terrifying. What is a breath-holding spell? Why do they happen and what can a parent do to prevent them?

A. The bad news about a breath-holding spell: "It's really scary for a parent to watch," says Dr. Jahn Avarello, division chief of pediatric emergency medicine at Cohen Children's Medical Center in New Hyde Park.

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The good news: "Almost all the time, it's really benign," Avarello says.

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Most of the time, a breath-holding spell is strictly a behavioral occurrence that happens in kids between 12 months and 3 years old, although it can happen as early as 6 months and as late as 6 years, he says. A child is upset by something, cries heavily and stops breathing until he or she passes out. Once the child passes out, however, breathing resumes. "Your brain is going to automatically make you start breathing again right away," Avarello says.

Usually parents call 911 and/or head to an emergency room the first time, Avarello says, which he recommends to rule out an underlying medical cause such as a heart defect. But once physical causes have been eliminated, the family is referred to their pediatrician, who will likely be equipped to discuss what to do to prevent or deal with future occurrences, Avarello says.

More bad news: The child might turn blue during an episode. "That scares the living daylights out of people," Avarello says. Rarely, the child could have a seizure, which also typically is benign but frightening, he says. This can make parents give in to children's demands for fear of another episode, which can worsen the problem.

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Online literature and advice from professionals can help parents cope. The episodes will likely stop by age 3, he says.