Last reviewed by Faculty of Harvard Medical School on January 24, 2013
By Harvey B. Simon, M.D.
Harvard Medical School
Here's something the iPod generation doesn't wants to hear about: acoustic trauma or noise-induced hearing loss.
When we are exposed to sounds that are too loud or loud sounds that last a long time, we can lose hearing. Acoustic trauma is the most important preventable cause of permanent hearing loss. Find out who's at risk, what the warning signs are and how loud noises may affect your heart. This is one message that should ring out clear (if not loud).
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Noise-induced hearing loss is a product of modern life. It first appeared during the Industrial Revolution when workers were exposed to loud machinery for hours on end. Exposure at work is still the most common cause of acoustic trauma, but recreational noise threatens to catch up.
When this problem was first recognized, it was called boilermakers' disease because of the impaired hearing that plagued men who made steam boilers. If present trends continue, though, it may someday be known as "iPod ear."
About 15% of Americans between the ages of 20 and 69 or 26 million Americans have hearing loss that may be due to harmful noise.
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How Loud Sounds Damage Hearing
The ear is divided into three parts. Sound waves first enter the outer ear, which acts as a sound-collecting channel. Next, the waves strike the tympanic membrane or eardrum, causing it to vibrate. The vibrations are transmitted through the middle ear along a short chain of three small bones: the hammer, anvil and stirrup. Finally, these vibrations reach the cochlea in the inner ear, which is lined by tiny hair cells, the cilia. The vibrations caused by sound produce a shearing force on the cilia. The cilia then translate the sound into electrical signals that travel along the acoustic nerve to the brain.
When it comes to loud sounds, the delicate cilia are the weak link. Very loud sound produces excessive force that can damage the hair cells. The cells can recover from mild damage, but severe damage will kill nerve cells. This leads to permanent hearing loss.
Extremely loud sounds will damage anyone's ears, but some people are more susceptible than others. Genetics and environmental factors, such as smoking and exposure to heavy metals and solvents, can play a role. Still, in the last analysis it is the sound itself that can damage the fragile hearing structures.
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How Loud Is Too Loud?
Sound is measured in decibels (dB). The higher the number of decibels, the louder the sound. An increase of just 3 dB indicates a doubling of the sound intensity.
How much sound is dangerous to your hearing? The Occupational Safety and Health Administration (OSHA) has developed guides based how long the sound lasts as well as how loud it is. For example:
- Sounds below 75 dB are safe, but eight hours of exposure to sounds at just 85 dB can be harmful.
- Just four hours of noise at 88 dB will deliver the same dose of sound as eight hours at 85 dB.
- A single gunshot at 140 dB will be as damaging as 40 hours at 90 dB.
OSHA requires hearing protection programs for workers exposed to this level of sound.
Most often, noise-induced hearing loss begins with a subtle difficulty in hearing high-frequency tones. If the exposure continues, hearing loss gradually affects lower tones and becomes more severe. Both ears are usually affected equally, but if one ear is closer to the offending sound, it will suffer more damage.
Once you lose your hearing, it can't be restored. Your only recourse is a hearing aid, which increases whatever little sound your acoustic nerve can still pick up. That's why it's very important to recognize early symptoms of hearing loss, such as:
If you allow the noise exposure to continue, you're likely to suffer permanent hearing loss.
If you're exposed to loud noises, you are vulnerable. If you have to shout to make yourself understood by someone just an arm's length away, then the noise that's forcing you to raise your voice is loud enough to be damaging.
But exposure at work is the most common cause of noise-induced hearing loss. Construction workers, factory workers, policeman, firefighters, military personnel, farmers and truck drivers are often victims. Enthusiastic crowds at sporting events can also generate excessive sound, putting stadium workers and fans who attend many games at risk.
Personal stereos are a particular threat to the younger generation. Batteries last longer, which means people can listen for hours on end. iPods can store lots of music for continuous listening. Listeners are conditioned to like loud music. Because they often listen to their music in public, they are likely to turn the volume even higher to drown out competing background sounds. The trendy ear buds that are replacing bulky headphones make the problem even worse by focusing the sound directly into the ear.
Noise-induced hearing loss is completely preventable. Here's how you can protect your hearing: