Joe is a patient here at Earlux. He is 52 years old and has been a firefighter his entire adult life. A few years ago, his wife began complaining that he didn’t seem to be listening to her, and around the same time, he started to turn down invitations to go out to eat with friends and family, because in noisy restaurants, he just couldn’t understand what people were saying to him and it wasn’t fun to be left out. When he first came to us for help, he was skeptical about hearing aids; he told us that he could hear just fine, and that clarity was the issue. He also told us that he thought he was too young for hearing aids.
Linda is another of our patients. She is 70 years old and lives a quiet life now, but this wasn’t always the case. For many, many years, Linda spent her weekends at concerts and music festivals and figured that the ringing in her ears at the end of the night just meant she’d had a good time. These days, that ringing in her ears is constant. She came to us because she felt like the ringing itself was what was interfering with her ability to understand what her young grandkids were telling her.
What Joe and Linda have in common is noise-induced hearing loss. Well over 30 million Americans have noticeable hearing loss caused by exposure to loud noise, and a recent study by the CDC showed that even among people without significant hearing loss, a high proportion show evidence of noise damage. We live in a noisy world: consider how many loud vehicles, sirens, machines, music, and incidental sounds you encounter on a daily basis. Over time, this noise exposure can add up and affect nearly everyone’s hearing to some extent. The people most likely to experience noise-induced hearing loss are, of course, those whose noise exposure goes above and beyond the average – people like Joe, who has spent decades driving a fire truck with the siren on and the window down, and Linda, who loved the way she could feel the sound waves shaking her whole body and never stopped to think about the damage she was incurring. But many of the people we see with obvious clinical signs of noise damage don’t realize that they’re around a dangerous level of noise. Their noise exposure comes from regular, everyday sources: mowing the lawn, drying their hair, and driving a truck. If only they’d better understood how to take care of their hearing!
October is National Protect Your Hearing Month. To “celebrate,” Earlux is planning a two-part series on noise-induced hearing loss; this article will cover the causes and effects of noise damage, and the second will cover prevention and protection.
What actually happens to your ears?
To understand how loud sounds can actually damage your hearing, it’s important to understand how you hear sound in the first place. We’ll keep it simple, don’t worry! First, you need to know that sound is a vibration in the air. This vibration enters your ear canal and hits your eardrum, which itself begins vibrating and transmits the sound to your middle ear. The middle ear’s main role is to amplify those vibrations and deliver them to the inner ear, or cochlea, which is where the sensory cells are located.
The inside of the cochlea – that snail-shaped part of the ear that you may have seen diagrams of – contains fluid as well as the actual hearing organ, which is called the Organ of Corti. We’ll skip the granular detail here, but if you’re interested, you can start with a resource like this one. The critical thing to know about the Organ of Corti is that it contains the stereocilia, or hair cells, which bend when they’re hit by the vibration (sound) and transmit the signal up the auditory nerve to the brain. Only when your brain receives the signal do you actually perceive the sound!
Now, back to those vibrations in the air. Louder sounds mean bigger vibrations. Think of Linda, standing in front of the speakers at those concerts, feeling the bass with her whole body. When such huge vibrations get to the inner ear and bend the hair cells, it isn’t gentle. Those poor little cells are violently knocked over, and while they can heal at first, repeated exposure to this sort of violence will eventually be too much to bear, and they will sustain permanent damage. Images of damaged inner ears show broken-down or even missing hair cells. Of course, those damaged cells are now much less sensitive to smaller vibrations, which is why folks with hearing loss can’t hear certain soft sounds – those damaged cells need to be hit harder before they’ll send the signal up the nerve.
Age-related hearing loss is similar, but the damage to the hair cells is caused by breakdown over time, rather than specific trauma. Of course, no one lives in isolation from loud sound (and no one is immune to aging!), so noise exposure typically contributes to age-related hearing loss and aging typically contributes to noise-induced hearing loss. This is part of why noise damage doesn’t always show up right away: consider Vietnam veterans, many of whom were exposed to truly excessive noise, but didn’t have noticeable hearing loss right when they got home. Decades later, though, having served in the war absolutely means those guys are more likely to have hearing loss than they otherwise would have been.
How much noise does it take?
According to the National Institute for Occupational Safety and Health (NIOSH), which is a government agency charged with recommending occupational health and safety standards, the maximum permissible noise dose is 85 decibels averaged over an eight-hour period. The Occupational Safety and Health Administration (OSHA) is the regulatory agency that sets legal limits on noise exposure in the workplace – NIOSH doesn’t have the power to enforce, only to recommend – and it has set the maximum permissible dose as 90 dBA over an eight-hour period, or higher than that for shorter periods of time, such that a worker is allowed to be exposed to 110 dBA for 30 minutes.
Unfortunately, your ears don’t really care what a government agency has deemed acceptable, and this amount of sound can absolutely be damaging if you’re exposed to it day in and day out. Folks who work in manufacturing plants with loud machinery may be exposed to a legal amount of noise and still suffer noise-induced hearing loss, and, in fact, this is a common story that our hearing loss patients tell. Furthermore, there isn’t a bright line between a safe amount of noise and a damaging one, because people aren’t all the same. There are differences in genetic susceptibility from one person to another, meaning that two people who are exposed to the exact same amount of noise over their lifetimes will end up with different degrees of hearing damage. A good rule of thumb is that if you have to shout to be heard over the noise, it’s too loud.
A few examples of dangerously loud sounds:
- Some vacuum cleaners
- Dental drills
- Garbage disposals
- Leaf blowers
- Driving on the highway with your window down
As you can see, many everyday sounds are too loud for your hearing health!
Noise-induced hearing loss: what is it like?
When you see an audiologist for a hearing test, your results will be shown on a graph called an audiogram. This will show what decibel level is needed for you to just barely detect a tone at each of the tested frequencies in each ear. Normal hearing will look like a straight line across the top, with each marked threshold being better than 20 dB.
With noise-induced hearing loss, the audiogram will begin to show hearing loss in the high frequencies first. In fact, the common configuration associated with noise damage is a notch, most often centered around 4000 Hz but sometimes around 3000 or 6000 Hz, where the thresholds above and below that point are better. With very early noise damage, you may not notice any trouble with your hearing at all, but this notch pattern can still be evident. In some cases, all thresholds are technically “normal,” but if most of your thresholds are at 5 decibels and then at 4000 Hz it’s 15 decibels, you have the beginnings of noise-induced hearing loss.
As age begins to contribute to hearing difficulties, the notch may become less evident, and the audiogram may show a simple high-frequency hearing loss without the characteristic recovery in frequencies higher than the center of the notch. This is still noise-induced hearing loss, but the noise exposure is only one factor.
When you have noise-induced hearing loss, you will most likely struggle with speech clarity. Different sounds of speech occur at different frequencies, and the soft little consonant sounds that are just air – “f,” “s,” “th,” and the like – are high-frequency sounds that are the first to go when you have a high-frequency hearing loss. If your low frequencies are still normal or near normal, you will perceive loudness perfectly normally, leading to descriptions like we heard from Joe earlier: “I can hear just fine, but it isn’t clear.” Background noise makes this problem worse, and noise-induced hearing loss causes particular difficulty with background noise, as the damage to your auditory system makes it hard to separate the sounds you want to hear from the sounds you don’t.
Some people with noise exposure can experience difficulty in background noise even when their audiogram (hearing test) doesn’t indicate hearing loss at all. This is a phenomenon known as hidden hearing loss, and it is thought to be caused by cochlear synapse dysfunction associated with noise exposure. (This may be a topic for a future article!)
Another, very well-known effect of noise exposure is tinnitus. This is that annoying ringing or buzzing in your ears that no one but you can hear. It’s common to hear it just after being exposed to a damaging level of noise – remember our example patient, Linda, leaving a really good concert with her ears ringing and thinking it meant she’d had a great time. Oftentimes, acute tinnitus such as that will fade within 24 hours, but over time it may become constant. Contrary to what people like Linda believe, the tinnitus itself doesn’t interfere with the ability to hear; rather, the tinnitus and the difficulty hearing/understanding are both effects of damage to the auditory system. There is no medical cure for tinnitus. Wearing hearing aids, if you need them, is the most effective treatment for tinnitus, and there are other therapies available that can help reduce the perception of tinnitus, but once you’ve got tinnitus it tends to stick around.
Noise-induced hearing loss is a common affliction, and along with aging, is the main reason people develop hearing difficulties. This article has discussed the mechanisms that cause noise-induced hearing loss, as well as the symptoms. The next article in this series will talk about what you can do to prevent it. There is no cure for this type of hearing loss, nor for tinnitus, so the best thing you can do for your hearing health is to prevent the damage from occurring in the first place! Stay tuned!