More than two-thirds of young people who regularly use MP3 players face premature hearing damage because the volume is too high, a charity warns.
Listening volume should be below 85 decibels
The Royal National Institute for Deaf People said its findings were alarming, particularly with eight million MP3 players sold last year alone in the UK.
It accused manufacturers of failing to put clear and prominent warnings on packaging for consumers.
RNID urges MP3 player fans to invest in in-ear filters for headphones.
These cancel out background noise and reduce the need to increase volume levels.
The charity's latest research found that 72 out of 110 MP3 users tested in Brighton, Manchester and Birmingham were listening to volumes above 85 decibels.
That is noise equivalent to a loud alarm clock at close proximity.
The World Health Organization says that listening to earphones at 85 decibels or more for over an hour at a time can damage hearing.
RNID found that almost half of young people who use MP3 players listen for more than an hour a day, with a quarter listening for more than 21 hours a week.
And 58% of those surveyed were unaware of any risk to their hearing from using MP3 players and 79% had never seen warnings about noise levels on the packaging of MP3 players.
A quiet room at night - 20 decibels
An ordinary spoken conversation - 60 decibels
A busy street - 70 decibels
A pneumatic drill - 100 decibels
Some personal music players (at high volume) - 105 decibels
Aircraft taking off - 110 decibels
Listening to earphones at 85 decibels or more for over an hour at a time can damage hearing
The results echo those found by the charity when it conducted similar research 12 months ago.
An RNID spokeswoman said that last September they had written to 55 manufacturers of MP3 players and mobile phone manufacturers asking them to put clearer on pack warnings about the dangers of listening to their products at high volumes.
"We heard back from two."
Brian Lamb, acting chief executive of RNID, said: "MP3 manufacturers have a responsibility to make their customers aware of the dangers by printing clear warnings on packaging and linking volume controls to decibel levels.
"It's easy to crank up the sound levels on your MP3 player to damagingly loud levels, especially on busy streets or public transport.
"But if people can hear the music from your headphones from just a metre away, you're putting your hearing at risk."