Q: My son's 9-year-old friend was recently diagnosed with obsessive-compulsive disorder, and I'm having a hard time explaining it to my son. What can I tell him to help him understand his friend's behavior?

Q: My son's 9-year-old friend was recently diagnosed with obsessive-compulsive disorder, and I'm having a hard time explaining it to my son. What can I tell him to help him understand his friend's behavior?

A: All kids have worries. But kids withobsessive-compulsive disorder(OCD) often can't stop worrying, no matter how much they try. Those worries make them behave in certain ways. A: All kids have worries. But kids with(OCD) often can't stop worrying, no matter how much they try. Those worries make them behave in certain ways.

OCD involves excessive worrying or thinking about something despite efforts to stop thinking about it (obsessions), as well as having rituals, or things that one has to do in order to prevent something bad from happening (compulsions). OCD is like a false alarm. It makes a person worry about something that is not harmful.

Common obsessions include fear of contamination (dirt and germs), a need for symmetry, lucky and unlucky numbers, and a fear of illness or harm coming to oneself or to relatives.

Common compulsions include grooming (hand washing and showering), repeating (going in and out of doorways, rereading, rewriting) and checking (making sure something is turned off, checking homework/backpack). Other rituals may include ordering or arranging objects, counting, and hoarding or collecting things.

Treatment can significantly reduce symptoms. Parents should start with the pediatrician, who may recommend visiting a mental health professional to get an accurate diagnosis and determine the best treatment plan.

Remember, no one can "catch" OCD. Your son should feel comfortable continuing to hang out with his friend, even if he has worries.

-Heather Yardley, Ph.D., is a pediatric psychologist at Nationwide Children's Hospital.