Loud sound exposure from listing to music may be causing hearing problems among teens which rose nearly 30% in 15 years, a new study suggests.

The study, published in the Journal of the American Medical Association, analyzed national health data from the early 1990s and the mid 2000s.

In the first survey, about 15 percent of teenagers were found by trained staff to have some degree of hearing loss. Some 15 years later, that number had risen by a third, to nearly 20 percent -- or one in every five teenagers.

The researchers said the reasons for the rise were unclear as teenagers, when asked about noise exposure - on the job, from firearms or recreational activities, for instance - didn't indicate any change.

"Some risk factors, such as loud sound exposure from listing to music, may be of particular importance to adolescents," the report said.

The volume of music players can sometimes exceed 110 decibels, said Dr. John W. House, president of the House Ear Institute in Los Angeles. Standards set by the Occupational Safety and Health Administration require noise protection in workplaces for exposure to noise levels of 110 decibels for more than 30 minutes.

"The high-frequency hearing loss is most consistent with noise exposure," said House. "I think we're seeing that trend now because of iPods and other personal listening devices that teenagers listen to at high volumes for long periods of time."

The researchers did not single out personal listening devices or iPods for the growing problem.

Teens are encouraged to turn down the volume and take frequent breaks from listening to music.

"Listening devices are fine as long as the volume is at a reasonable level, and they're not listening to them for extended periods of time," said House.