Whether during a midday jog, a coffee shop study session or a clattery morning subway commute, Americans are increasingly using iPods to envelop themselves in their own environment and block out background noise. But a recent study found that over time, pumping up the volume for more than 90 minutes a day can cause hearing loss. This often happens gradually—it can be years before the damage is noticeable. How loud is too loud? “If someone standing three feet away can hear what you’re listening to, that’s too loud,” says Catherine Palmer, PhD, director of audiology at the University of Pittsburgh Medical Center. Experts typically recommend keeping the sound level near the middle of the range. But “sometimes, the train is so noisy, you keep turning it up,” Dr. Palmer observes. One alternative: noise-canceling headphones that block out the racket around you, allowing you to lower the volume. Pam Mason, an audiologist at the American Speech-Language-Hearing Association warns that these headsets only help people monitor the sound. “It doesn’t make it safer to listen loudly,” she says. Dr. Palmer also advises users to remain aware of their surroundings.