WASHINGTON (Reuters) - So your teen-ager comes home with her eyebrow pierced -- should you be worried, or glad that she didn't do something worse?

A report released at a conference this week suggests a parent should be very worried because high school students with body piercings tend also to have smoked, used alcohol, had sex, skipped school and gotten into fights.

The study, by Dr. Timothy Roberts of the University of Rochester in New York, shows clear links between body piercings -- other than the ears -- and risky behavior.

"It's just like hairstyle, cosmetics, jewelry -- these are things an adolescent uses to project an image of him or herself to the world," Roberts said in a telephone interview. "They can give you a lot of clues about how an adolescent sees himself."

And while body piercing is becoming more mainstream, in a teen it still signals rebellion.

Roberts, a pediatrician, told a meeting of the Pediatric Academic Societies in Baltimore that he studied information on nearly 4,600 teens aged 12-19 taken in a U.S. government survey in 1995 and 1996.

The teens, living across the nation, were asked detailed questions about their behavior.

"Females (with body piercings) were about 2-1/2 times more likely to have had sex, 2-1/2 times more likely to have smoked, 2-1/2 times as likely to have used marijuana in the past month, and almost two times as likely to have skipped school in the last year."

Boys with piercings were five times as likely to have skipped school in the past year, and had similarly higher risks for smoking and drinking as girls.

Roberts said that body piercings did not guarantee that a child was misbehaving, but they should serve as a warning to parents, pediatricians and other health care providers.

"If your adolescent wants to have a body piercing, it is a reason to talk to them," he advised.

At the least, he or she should get it done properly. "Encourage them to get it done in safe, sanitary manner. Watch someone else get one. Do they have an autoclave, a machine to sterilize equipment? Do they use one needle and then throw it away?"

Roberts did a study last year that showed a very strong association between tattoos and risky behavior in teens.

"This doesn't apply to adults," he cautioned. "We didn't look at the effects of piercing on college-age people."