Noise-induced hearing loss (NIHL) is damage to hearing due to longtime exposure to harmful levels of noise, or a one-time exposure to noise at extreme decibels. NIHL is fairly common and many public health experts worry it's happening to more people at younger ages due to listening to music at damaging volumes with the use of headphones. It's estimated that at least 10 million Americans have hearing loss due to noise exposure.
What is noise?
Sound is what we hear when vibrations from the source travel through the air and reach our ears. Noise is defined as unwanted sound.
Sound quiet library, whispers rainfall normal conversation alarm clock, loud traffic, washing machine hair dryer, lawn mower, heavy city traffic passing motorcycle hand drill, snowmobile snow blower, MP3 player at max volume rock concert, chainsaw passing sirens jet plane taking off gun shot, fireworks at 3 ft.
Mechanisms of NIHL
To understand how noise-induced hearing loss works, it's first important to know how hearing works. Sound waves enter the outer ear and travel through the ear canal. The waves reach the eardrum, which sends vibrations to the three middle ear bones called the malleus, incus and stapes (also known as the hammer, anvil and stirrup). These bones amplify and transmit the sounds via vibrations to the fluid in the cochlea. The fluids of the cochlea bend the receptors of tiny hair cells, triggering electrical signals in the auditory nerve, which travel to the brain. The brain translates these signals into the sounds that we perceive and (usually) understand.
In the presence of sounds that are too loud, the vibrations get larger, causing fluid motion in the cochlea that can bend the hair cells to the point of breaking. Hair cells are not replaceable structures. Damaged hair cells are unable to trigger electrical signals to the brain, impeding hearing. Both intense but short noises - such as a nearby gunshot - and repeated or continuous exposure to loud noises - such as operating construction equipment - can damage the hair cells.
Causes of NIHL
|Did you know agriculture, construction, carpentry, mining and military occupations run the highest risk of high noise exposure?|
The workplace is the most common site of NIHL for most Americans. Jobs with the highest risk of noise exposure include:
- Agriculture: There are many sources of potentially damaging noise on farms. For example, tractors, combines, grain dryers, crop-dusting aircraft and orchard sprayers can register between about 80 and 115 dB. Even pig squeals are dangerous, measuring between 85 and 115 dB!
- Construction and Carpentry: NIHL is a very obvious hazard of construction work, and according to the CDC, 44 percent of carpenters and 48 percent of plumbers report being hard of hearing.
- Mining: According to the CDC, nearly 50 percent of miners will have hearing loss by age 50, which is drastically higher than the 9 percent of the general population. Additionally, 70 percent of miners will be hearing-impaired by age 60.
- Military: According to recent news reports, NIHL is the most common injury of returning war veterans in the U.S., due to the risks of close-combat fighting, bombs and artillery fire. According to a 2009 news report by The Guardian, 69 percent - or more than two-thirds - of Royal Marine commandos returning from war in Afghanistan were affected by NIHL.
American law - through the Occupational Safety and Health Administration (OSHA) - requires that employers take precautions to limit employees' hazardous noise exposure, including providing hearing protection equipment, maintaining machinery, placing barriers or isolating the noise source and developing a hearing conservation program to test employees' hearing and make sure they are protected. You can find the OSHA regulations online. If you are provided hearing protection at your place of employment, take it very seriously. Noise-induced hearing loss can be prevented!
There are things we do for fun that can also cause NIHL, including snowmobiling, shooting at a firing range, hunting, attending concerts, listening to extremely loud music and riding motorcycles.
Motorcycling can be damaging in several ways. For example, in a test of 33 motorcycles by audiologists at the University of Florida, they found that over half produced noise above 100 decibels when throttled. This level of noise exposure is only safe for up to 15 minutes according to OSHA. Even more dangerous to hearing, however, is surprisingly the use of helmets - wind noise is constant, and it rushes around the helmet, creating pressure variations. At only 55 miles per hour, the wind noise a motorcyclist is exposed to can reach 90 dB. However, traveling between 75 and 80 miles per hour, wind noise is around 105 dB. Helmets are a must for safety reasons, so motorcyclists should also protect their ears by wearing earplugs.
Attending loud concerts, being a musician and listening to music at loud levels are all possible sources of NIHL. According to one study by the Australian government, 20 percent of participants listened to portable music devices at potentially damaging levels. Additionally, a study from the Netherlands showed that 50 percent of adolescents using earphones utilized high-volume settings, and only 7 percent had a noise-limiting device.
Here are some concerning symptoms that should spur you to get your hearing tested by an audiologist:
You have trouble understanding what other people are saying, or it sounds like they are mumbling. This could be worse in crowded places. This could suggest high frequency hearing loss, which affects certain sounds only.
You have pain in your ears, even a few hours after loud noise exposure.
Other people comment that you're talking loudly or shouting.
You have tinnitus - ringing, whooshing, roaring or buzzing sounds in your ears.
Other effects of loud noise exposure
Aside from damaging the hearing, loud noise exposure and NIHL can lead to:
- Insomnia, even after noise stops
- High blood pressure
- Increased heart rate
- Isolation due to hearing loss
- Depression due to hearing loss
Noise-induced hearing loss is usually permanent, so it's important to take precautions to protect your ears. There are several solutions available for people who anticipate being in loud noise situations, including:
- Earplugs, which are placed in the ear canal and totally block it. Earplugs can be purchased at drug, hardware and sports stores. They come in different shapes and sizes and typically lower noise levels by 15 to 30 decibels, which is beneficial in most situations, but not all. Earplugs can also be custom-molded to fit your ears at an audiologist's office.
- Earmuffs, which fit completely over the ears and form a seal to block sounds between 15 and 30 dB. Many people pair earmuffs and plugs together for better sound reduction.
- Replacing loud machine parts and using lubricant to reduce friction and lower noise. Many cars, farm equipment and other machinery have mufflers, silencers and bearings that can lessen sound.
- Turning the music down. Many people listen to very loud music through headphones inserted in their ears. Be conscious of how loud your music is. Never use music to block out other sound.
Do whatever you can to avoid loud noise, including crossing the street rather than walking past a noisy construction site, or even plugging your ears.
Research and treatment
There are currently no effective treatments for noise-induced hearing loss or for regenerating the damaged hair cells in the cochlea, though there is some potentially promising research. Thus, it's important to do what you can to protect your hearing now.
- Noise Induced Hearing Loss, National Institute on Deafness and Other Communication Disorders, http://www.nidcd.nih.gov/health/hearing/pages/noise.aspx
- How Loud is Too Loud? How Long is Too Long?, It's a Noisy Planet, http://www.noisyplanet.nidcd.nih.gov/info/Pages/howloud.aspx
- Work-Related Hearing Loss, Centers for Disease Control and Prevention, http://www.cdc.gov/niosh/docs/2001-103/