WASHINGTON - Does your teen show normal nerves about the weekend party, or always stay home?

Nearly half of teenagers say they're shy, perhaps a bit surprising in our say-anything society. But a government study finds a small fraction of those teens show signs of a troubling anxiety disorder that can be mistaken for extreme shyness.

The report challenges criticism that the terms "social phobia" or "social anxiety disorder" medicalize normal shyness.

"Shyness is a normal human temperament," says lead researcher Dr. Kathleen Merikangas of the National Institute of Mental Health, whose teachers always noted her own childhood shyness on her report cards.

But just as it can be hard to tell when feeling sad turns into depression, "there is a blurred boundary between people who describe themselves as shy and clinically significant impairment," Merikangas adds.

The difference: The shy can be drawn out and adapt, while teens or adults with full-fledged social anxiety become so paralyzed during social situations that it interferes with everyday functioning.

"I didn't go out on dates or do any of the things that other kids did," recalls Cynthia Kipp of Tehachapi, Calif., who shared her story of years struggling with social phobia with the Anxiety Disorders Association of America. Now 48, she thinks her first anxiety symptoms began in fourth grade, when she can remember hiding under her coat in class, but worsened in high school when she tried drugs and alcohol for relief. Eventually she found treatment that worked.

The report also opens a window into the broader field of temperament research. Even garden-variety shyness worries parents, particularly fathers of boys, says Dr. Nancy Snidman of Children's Hospital Boston.

In school-age boys especially, "shyness isn't very well tolerated in the United States," says Snidman who wasn't involved with the new research.

Snidman and colleagues at Harvard Medical School have tracked infants to their college years, and know that babies who react very negatively to new people and objects tend to grow into shy children. That's not a bad thing - caution is considered an important evolutionary adaptation.

Usually, the clinging tot does just fine as he or she grows older and finds a niche, Snidman says. Girls may think the shy teen boy is nice because he's not macho, for example, or the shy kids wind up on the school newspaper so they can write instead of do public speaking. Many outgrow their shyness.

Yet a very shy child is considered more at risk than others of later developing some type of anxiety disorder - just as the opposite extreme, a very outgoing child, can be at greater risk for attention or conduct disorders, she says.

The new study, published by the journal Pediatrics, is based on in-person surveys of more than 10,000 U.S. teens about a variety of mental health issues. More than 6,000 of their parents were surveyed, too.

About 47 percent of the teens identified themselves as shy around peers they don't know well. More than 62 percent of parents thought their teens were shy, perhaps a reflection of parental worry.

Then Merikangas' team analyzed how many teens appeared to meet the American Psychiatric Association's criteria for social anxiety disorder or social phobia. Roughly 1 in 10 of the self-described shy kids did.

Social phobia tends to appear during adolescence when kids take their first real steps toward independence, but there's little information about how often. The National Institutes of Health estimates it affects about 15 million adults.

The surveyed teens weren't formally diagnosed; Boston's Snidman cautions that what a specialist observes can be quite different from what a teen recalls.

Still, those identified as potentially socially phobic were more likely to have another mental health problem, such as depression or substance abuse. But they were no more likely than the other teens to be taking psychiatric medications.

There are anxiety-treating medications but the main treatment is behavioral therapy, exposing people very gradually to fear-inducing situations and teaching them coping techniques.

What's a worried parent to watch for? This isn't standard stage fright, where you get sweaty palms before a speech but each one you do becomes easier. People with social anxiety disorder experience a more out-of-proportion fear that can make them shake, their hearts pound, or even cause a panic attack during a range of social situations. They start avoiding those scenarios.

The question is whether an anxious or shy teen is doing things typical of that age - participating in class, getting together with friends, going to group activities, says Dr. Chris Mauro, a Duke University psychologist. Try to get them into a group, whether it's sports or music or Scouts, because belonging is protective, he says.

The NIH's Merikangas recommends keeping an eye on social media, too. Sure it encourages electronic communication, but it may further isolate those already on that path, she says.

Teachers may notice a problem first, and shouldn't single out kids who won't participate in class but encourage them through group activities, she advises.

Lauran Neergaard covers health and medical issues for The Associated Press.