Loud rock music contributed to hearing loss among baby boomers, but MP3 players are poised to make the problem much worse for the next generation.

These devices, which pump music through headphones directly into the ear canal, enable the user to overcome the rumble of the subway or the drone of an airplane engine without drawing angry shouts of "turn it down!"

As a result, they easily desensitize the user to dangerously high sound levels. A CD player and a Walkman do too, but MP3 players such as the iPod pose an additional danger.

Because they hold thousands of songs and can play for hours without recharging, users tend to listen continuously for hours at a time. They don't even have to stop to change a CD or a tape.

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Longer Listening, More Damage

Since damage to hearing caused by high volume is determined by its duration, continuous listening to an MP3 player, even at a seemingly reasonable level, can damage the delicate hair cells in the inner ear that transmit sound impulses to the brain.

"Studies have shown that people exposed to 85 decibels for eight hours tend to develop hearing loss," Brian Fligor, ScD, of Children's Hospital in Boston, tells WebMD. He found that all the CD players he examined produced sound levels well in excess of 85 decibels.

"Every time you increase a sound level by three decibels, listening for half as long will produce the same amount of hearing loss. The kid who cuts my grass uses an iPod. The lawn mower noise is about 80 to 85 decibels. If he likes listening to his iPod 20 decibels above that, he's in the range of 100-105 decibels. At that sound level he shouldn't listen for more than eight to 15 minutes."

But if he's like millions of other iPod owners, the boy probably listens for several hours a day, placing a large noise burden on his hearing even if he turns it down when he's not cutting grass.

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Put a Lid on It

Limiting the volume of MP3 players may seem like an obvious solution.

Devices, such as the Kid'sEarSaver, claim to reduce the sound output of listening devices, such as MP3 and CD players. Inventor Tom Metcalfe tells WebMD that Kid'sEarSaver reduces sound by more than 15 decibels.

"That's enough to give parents some peace of mind," says Metcalfe.

Also, France and other European countries have enacted laws that limit the volume of iPods and other devices to 100 decibels.

But Fligor believes such efforts produce a false sense of safety.

"Capping the volume focuses on the sound level, not the dose," he said. "If you set the cap at 100, that doesn't give you license to listen all day."

Besides, as soon as those European nations capped the sound level of iPods, web sites started providing detailed instructions on how to override that limit.

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Dealing With Denial

The simple fact is that young people like their music loud and seldom believe that hearing loss is a serious danger.

A recent study in Pediatrics reported that of the nearly 10,000 people who responded to a survey posted on the MTV web site, only 8 percent considered hearing loss "a very big problem."

That was below sexually transmitted diseases (50 percent), alcohol and drug use (47 percent) and even acne (18 percent). While 61percent said they had experienced ringing in their ears or other hearing problems after attending rock concerts, only 14 percent said they had used ear protection.

Even when they believe hearing loss is a danger, many young people still refuse to turn down the music.

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Music Dependency

"When I ask kids why they're not worried about hearing loss, they say they have faith that medical technology will find a way to restore their hearing," Deanna Meinke, chairwoman of the National Hearing Conservation Association's Task Force on Children and Hearing, tells WebMD.

Mary Florentine, an audiologist at Northeastern University, suspects that some young people actually have what she calls a loud music dependency disorder (LMDD).

"I asked people why they continued to expose themselves to loud music even though they knew it was harming their hearing, and they said they couldn't stop listening," says Florentine. "They said, 'When I stop listening I get sad and depressed, and then I go back to it because I can't take it after a while. I start listening again at moderate levels, but it doesn't do anything for me, so I start to listen at high levels.'"

In a study, Florentine and colleagues adapted a test normally used to identify alcohol dependency. For example, the question, "Do you feel you are a normal drinker?" became, "Do you feel you listen at normal levels?" Eight of the 90 participants who answered the 32 questions had scores in the same range as substance abusers.

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Hearing Loss Goes Unnoticed

Denying the danger of noise-induced hearing loss would not be so easy if loud music made the ears bleed, but the early symptoms tend to come on gradually.

"People may notice that voices sound muffled, and that they have a reduced ability to follow a conversation in a noisy environment such as a restaurant or a party," Andy Vermiglio, CCC-A, FAAA, a research audiologist at the House Ear Institute in Los Angeles, tells WebMD.

"They might hear ringing in their ears. In its worst form, the ringing can get so loud that it interferes with sleep."

While a routine hearing test administered by a doctor can reveal mild hearing loss, the problem may become advanced before people realize they're having serious difficulty hearing.

Hearing loss, which becomes more common with age, is creeping farther down the age spectrum.

Kids With Old Ears

An article in the journal Pediatrics estimated that 12.5 percent of children aged 6 to 19 -- about 5.2 million -- have noise-induced hearing loss.

"Our own research shows that 16 percent of 6-to 19-year-olds have early signs of hearing loss at the range most readily damaged by loud sounds," says William Martin, PhD, of the Oregon Health and Science University Tinnitus Clinic in Portland.

Because adolescents are so resistant to warnings about loud music, Martin is trying to raise awareness among younger children. He is co-director of the Dangerous Decibels Project, which, in conjunction with the Oregon Museum of Science and Industry in Portland, has developed a program designed to train children, parents, and teachers about the threat of noise-induced hearing loss. It stresses the three most practical ways to deal with loud noise: turn it down, walk away, or protect your ears.

But education merely raises awareness of the problem. As with the epidemic of obesity among the young, hearing loss will end only when young people themselves recognize the dangers and change their behavior.

"People have to use personal stereo systems wisely or they will rapidly accelerate the aging of their ears," says Martin. "You can't toughen your ears by listening. Some people think you can. But if it's loud enough for long enough, you're going to cause permanent damage to your hearing."

By Tom Valeo, reviewed by Michael W. Smith , MD

SOURCES: Brian Fligor, ScD, director, Diagnostic Audiology, Children's Hospital, Boston; instructor, Harvard Medical School. Chung, J. H. Pediatrics. April 2005; vol 115: pp 861-867. Tom Metcalfe, founder, Kid's Ear Saver Co. Deanna Meinke, chairwoman, National Hearing Conservation Association's Task Force on Children and Hearing; assistant professor of communication disorders, University of Northern Colorado. Mary Florentine, Matthews Distinguished Professor of Audiology, Northeastern University, Boston. Florentine, M. Ear & Hearing. December 1998; vol 19: pp 420-428. Andy Vermiglio, MA, CCC-A, FAAA, audiologist; senior research associate, House Ear Institute, Los Angeles. William Martin, PhD, director, Oregon Health and Science University Tinnitus Clinic, Portland; co-director, Dangerous Decibels Project. National Institute on Deafness and Other Communication Disorders web site. Niskar, A.S. Pediatrics, July, 2001; vol 108: pp 40-43.