Up to a quarter of iPod users have listening habits that can damage their hearing, research shows.
The US-based study also found asking a teenager to turn down their MP3 player could have the opposite affect, while teens who voiced the most concern about hearing loss often played their music the loudest.
"We really don't have a good explanation for why teens concerned about hearing loss risk actually play their music louder than others," said doctoral candidate Cory Portnuff, of the University of Colorado.
"But we do know that teens who knew what the benefits were of listening at lower levels had less hearing loss risk, which is why we believe targeted education is the key."
The study found teenage boys generally listened to their personal MP3 players at a higher volume than girls. Teens played their music louder than young adults did, and teens may inaccurately perceive how loudly they were playing their music.
Portnuff said risky iPod listening was determined by time as well as volume, plus a third less quantifiable factor – ear sensitivity.
Some people were born with "tougher ears" that allowed them to listen safely for longer periods, he said, while others had "tender ears" and could suffer damage even if they followed the recommendations.
That said, Portnuff's study concluded between 7.0 to 24 per cent of teens were listening to their iPods and MP3 players at risky levels.
"We don't seem to be at an epidemic level for hearing loss from music players," he said.
An earlier study, in 2006, found a typical person could safely listen to an iPod for 4.6 hours per day at 70 per cent volume using stock earphones.
At 80 per cent of volume, the safe listening time was 90 minutes a day but, at full volume, this dropped to just five minutes.
Portnuff said the latest research echoed the results of similar studies 20 years ago when Walkman audio cassette players first entered the market.
"(However) one of the concerns we have today is that while Walkmans back then operated on AA batteries that usually began to run down after several hours, teenagers today can listen to their iPods for up to 20 hours without recharging them," Portnuff said.
The qualitative study included about 30 volunteers and the results were presented at Atlanta's annual Hearing Conservation Conference.
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