Narrator:        This is Science Today. It's probably fair to bet that at some point or another, everybody has been guilty of cranking up the volume on their MP3 players. The question is — for how long? Jeff Carroll, a graduate researcher of the University of California, Irvine's Center for Hearing Research, says one of the issues with MP3 players is duration.

Carroll:           Sounds that are somewhat comfortable for a short period of time, if listened to long enough can cause permanent damage and because of the battery life of MP3 players and how popular they've become, you have people that are listening to sound input at 80-85 decibels for 12 hours a day and that's where you start to see some permanent hearing loss.

Narrator:        Carroll has been studying the safety of different devices that are commercially available on the market, including toys and video games that are set up to be used on MP3 players.

Carroll:           The main trade-off is still sound level versus amount of time. The louder it is, the shorter you can listen to it.

Narrator:        For Science Today, I'm Larissa Branin.