The surge in sales of iPods and other portable music players in recent years could mean many more people will develop hearing loss, experts fear.
The iPod is the world's most popular digital music player
If the volume through headphones is too high, there is a real risk of permanent damage to hearing, they say.
Sydney's National Acoustic Laboratories found a quarter of personal music system users in a random sample listened to music at dangerous volumes.
The Royal National Institute for Deaf people urged awareness of the risks.
Millions now own MP3 players - Apple has sold more than 20 million iPods.
A recent study by the Royal National Institute for Deaf People (RNID) found 39% of 18 to 24-year-olds listened to personal music players for at least an hour every day and 42% admitted they thought they had the volume too high.
The RNID regards 80 decibels as the level at which hearing is threatened - 20 less than a pneumatic drill.
Some MP3 players can reach 105 decibels. EU iPods have a sound limiter to comply with noise safety levels, however sometimes users hack through this in order to listen to it louder.
The RNID said it was possible that any rise in popularity of personal music players might lead to more cases of hearing loss in the future.
A spokesman said: "RNID has been concerned for some time that many people are turning up the volume on their personal stereos to levels that could create hearing loss in the long term.
"This is precisely the case when attempting to drown out unpleasant noise from traffic and on the Tube."
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
Graham Frost, chairman of the British Society of Audiology, said the risk of damage increased with noise level and duration of use of personal music systems .
He said it could take months or years for that become apparent to the individual.
"Users are using them for longer periods because of the amount of material stored on them and because of convenience.
"If you use them for short periods and have breaks in between that is better than continuous use."
The first warning sign that volumes might be too high is a ringing or buzzing noise in the ears, says the RNID.
It is a sign the sound was loud enough to damage your ears, if exposure became frequent.
Protective filters for in-ear headphones are available from many high street stores and regular breaks should be taken from listening to personal stereos.
Apple was unavailable for comment.
RNID has a campaign urging people to be aware of the risks so they can continue to enjoy music for longer.
Don't Lose the Music Campaign recommends:
- Take regular breaks from the dance floor in nightclubs and use club chill out areas to give ears a rest from loud music
- Stand away from loud speakers when in clubs or at gigs and concerts
- Wear ear plugs if regularly exposed to loud music, i.e. as a frequent clubber, DJ or musician