Posted: Monday, Aug. 31, 2015 --- 12:24 p.m.
(NBC News)--- Doctors warn that a steady onslaught of loud noise, particularly through ear buds, is damaging the hearing of a generation wired for sound, although they may not realize it for years.
More than 1 billion young people are at risk of hearing loss because of personal audio devices, such as smartphones, and damaging levels of sound at entertainment venues like electronic dance music festivals, where noise levels can top 120 decibels for hours, according to the World Health Organization.
"Probably the largest cause [of hearing damage] is millennials using iPods and [smartphones]," says Dr. Sreekant Cherukuri, an ear, nose, and throat specialist from Munster, Indiana and founder of MD Hearing Aid.
Hearing loss among today's teens is about 30 percent higher than in the 1980s and 1990s, Cherukuri estimates.
"You (once) had a Walkman with two AA batteries and headphones that went over your ears," he told NBC News. "At high volume, the sound was so distorted and the battery life was poor. Nowadays, we have smart phones that are extremely complex computers with high-level fidelity."
Cherukuri tells young patients to stop wearing headphones — especially earbuds, which place the sound closer to the ear drum, enhancing volume by as much as 9 decibels.
"It's very easy to achieve unknowingly," he said.
The damage happens when sound travels from the earbud deep inside your ear to the cochlea, where some 20,000 hair cells transmit the sound to the brain. But if the sound is too loud, and listened to for too long, it can damage those hair cells, or worse, cause them to die off.
Any level over decibels, just over 50 percent volume on most smartphones, is considered harmful after 15 minutes, according to the National Institutes of Health.
Permanent damage can happen in minutes, experts say, and when the damage is done, it's irreversible.
"Noise exposure in kids is a growing concern," said Nicole Raia, a clinical audiologist at University Hospital in Newark, New Jersey.
Raia said she sees more tinnitus in young people, an early sign of hearing loss, but, "we don't catch them until they are in their 20s and 30s."
And because audio-screening protocols are not that sophisticated, many children with subtle damage pass hearing tests, she added.
A study published in 2014 revealed that nerve synapses can be more vulnerable to damage than hair cells in the inner ear. When young animals were exposed to loud noise, even just once, they had accelerated hearing loss later in life.
"Within minutes of exposure, the points between the hair cells and the neurons were injured and the loss was permanent," said co-author Sharon Kujawa, director of the department of audiology at Massachusetts Eye and Ear Infirmary.
The problem is when there is exposure to excessive noise, it goes away within a few hours.
This "hidden" hearing loss is not picked up by standard threshold tests on which all national standards are based.
Experts say the best way to protect young ears is to apply the "60/60" rule: Keep the volume on the MP3 player under 60 percent and only listen for a maximum of 60 minutes a day.
When using headphones in a noisy place like a school bus or subway, the tendency is the turn the volume up, so use headphones that cover up outside noise.
And to protect your kids, use Apple's parental control setting to set lower sound levels on iPhones and iPods, locked in place with a password.
For small children at loud sporting events, music concerts or riding on the subway, buy ear protection.