Researchers compared hearing loss evaluated in two national surveys, one conducted in 1988-1994 and the other in 2005-2006. ''In the initial assessment back in the early '90's, about 15% [of teens] had any hearing loss," says researcher Gary C. Curhan MD, ScD, associate professor of medicine and epidemiology at Harvard Medical School and Harvard School of Public Health.
''More recently, it was 19%," he says.
''On a relative basis, that's about 30% higher," he tells WebMD. "Previously, one in seven children would have been found to have hearing loss. Now it's one of five."
The majority of the hearing loss found was slight, Curhan and his colleagues found. But, Curhan says, "any hearing loss is bad."
The study is published in the Journal of the American Medical Association.
Updating Data on Teen Hearing Loss
Curhan and his colleagues compared data from two surveys: the Third National Health and Nutrition Examination Survey (NHANES III) and NHANES 2005-2006.
The earlier survey included data from 2,928 participants; the second had data from 1,771 participants, all ages 12 to 19.
The earlier survey didn't include data on exposure to loud noise for five or more hours a week, but the later study did. In the 2005-2006 survey, 29% of respondents said they were exposed to such noise. But the researchers did not find a significant link between that and hearing loss.
Children from families below the federal poverty level did have a higher risk of hearing loss -- they were 1.6 times more likely than children from families above the poverty threshold to have hearing loss. While about 23% of children from the poorer families had hearing loss, about 18% of those in families above the poverty threshold did.
High-frequency hearing loss, which often occurs from noise exposure, was higher in the second survey than the first, the researchers found.
Even slight hearing loss in school-aged children can create a need for speech therapy and other special help, the researchers say. Mild loss can interfere with speech and language development, school performance, and impair social and emotional development.
Explaining Hearing Loss in Teens
The analysis didn't go into the reasons for the loss, Curhan says. They had speculated that greater use of vaccines (such as vaccination against Streptococcus pneumonia, a bacteriumthat can causeinfections leading to hearing loss) would lead to a reduction in hearing loss in teens.
But it did not.
The survey data didn't include data on the teen's use of personal listening devices. "We know very loud noises for long periods of time are harmful," Curhan says. Yet to give more specific guidelines for teen music listening is not possible, he says.
The new survey is concerning, says Robert K. Jackler, MD, Sewall Professor and Chair of Otolaryngology at Stanford University School of Medicine, who reviewed the study findings for WebMD.
''It certainly raises red flags," he says of the finding that one in five teens has hearing loss.
"This degree of increase is concerning," says Jackler, who is chair of the hearing committee for the American Academy of Otolaryngology -- Head and Neck Surgery.
While the researchers won't specify suspected reasons for the increase, Jackler suspects the increasing use of amplified music among adolescents.
The researchers found high-frequency loss much higher in the second survey, he points out, and that is the type that's often the result of excessive noise exposure as well as aging.
''If this study is validated, and if this trend is validated, it gives a strong argument in favor of limiting the ability of these amplified music players to deliver potentially injurious levels of noise," he tells WebMD.
In Europe, a proposed standard would have manufacturers of personal music players provide a safe “default” setting. Jackler suggests the U.S. government should consider adopting lower levels of maximum output.
How to Prevent Hearing Loss in Teens
What can parents do to help preserve teens' hearing?
Remind them to turn down the volume when listening to music, says Alison Grimes, an audiologist and manager of the audiology clinic at Ronald Reagan-UCLA Medical Center, Los Angeles, who reviewed the study findings for WebMD.
''If you can't turn down the volume, get physically further away from the sound, or use earplugs," says Grimes, who is also past president of the American Academy of Audiology.
How loud is too loud? ''The conservative approach would be to listen at 85 decibels or below," says Jackler.
That's about the noise you would hear, Grimes says, if you hold a hair dryer 6 inches from your ear.
Grimes suggests parents also tell teens to turn off the music for 10 minutes each hour and give their ears a break. Symptoms such as ringing in the ears or feelings of fullness, she says, ''are both signs the noise exposure has been too loud."
A telephone inquiry to Apple, which makes the iPod personal listening device, was not returned in time for publication.