Tel Aviv: One in four teenagers are in danger of early hearing loss as a direct result of listening to music on their personal listening devices (PLDs) like MP3 players and iPods.

Personal listening devices permit users to listen to crystal-clear tunes at high volume for hours on end, a radical improvement over Walkman.

But according to Tel Aviv University (TAU) researchers, these advances have also turned these devices PLDs into a serious health hazard, with teenagers facing the greatest risk.

One in four teens is in danger of early hearing loss as a direct result of these listening habits, says Chava Muchnik professor of audiology at TAU's Sackler Faculty of Medicine and Sheba Medical Centre, the International Journal of Audiology reports.

With colleagues Ricky Kaplan-Neeman, Noam Amir and Ester Shabtai, Muchnik studied teens' music listening habits and took acoustic measurements of preferred listening levels, according to a TAU statement.

The results demonstrate clearly that teens have harmful music-listening habits when it comes to iPods and other MP3 devices.

"In 10 or 20 years, it will be too late to realize that an entire generation of young people is suffering from hearing problems much earlier than expected from natural ageing," says Muchnik.

Those who are misusing MP3 players today might find that their hearing begins to deteriorate as early as their 30's and 40's - much earlier than past generations.

The first stage of the study included 289 participants aged 13 to 17 years. In the second stage, measurements of these listening levels were performed on 74 teens in both quiet and noisy environments.

The study's findings are worrisome, says Muchnik. Eighty percent of teens use their PLDs regularly, with 21 percent listening from one to four hours daily, and eight percent listening more than four hours consecutively.

Taken together with the acoustic measurement results, the data indicate that a quarter of the participants are at severe risk for hearing loss.