Noise Induced Hearing Loss (NIHL): Causes & Prevention
- Publish Date: 2016/02/15 - (Rev. 2016/10/11)
- Author: Thomas C. Weiss
- Contact : Disabled World
Outline: Long lasting and loud sounds can damage sensitive structures in the inner ear and cause noise induced hearing loss (NIHL).
Each day, people experience sound in their environments such as the sound from radio and television, traffic and home appliances. Usually, these sound are at safe levels that do not damage a person's hearing. Yet sound may be harmful when they are too loud - even for a short period of time, or when they are both long-lasting and loud. The sounds might damage sensitive structures in a person's inner ear and cause noise induced hearing loss (NIHL).
Noise-induced hearing loss (NIHL) is defined as a hearing impairment resulting from exposure to high decibel sound that may exhibit as loss of a narrow range of frequencies, impaired cognitive perception of sound or other impairment, including hyperacusis or tinnitus. Long term exposure to sound levels over 80 dB can cause permanent hearing loss. Once lost, hearing cannot currently be restored in humans.
NIHL can be immediate, or it can take a long time before a person notices it. It may be temporary or permanent and it may affect one or both of a person's ears. Even if someone cannot tell that you are damaging your hearing, you might have difficulties with hearing in the future, such as an inability to understand other people when they speak; particularly in a noisy room or on the telephone. Despite the way it may affect someone one thing is for sure, noise induced hearing loss is something a person can prevent.
Exposure to harmful noise can happen at any age.
People of all ages - to include children, adolescents, young adults and seniors can develop NIHL. Around fifteen percent of people in America between the ages of twenty and sixty-nine, or twenty-six million Americans, experience hearing loss that might have been caused by exposure to noise either at work or during leisure activities. As many as sixteen percent of teenagers between the ages of twelve and nineteen have reported some level of hearing loss that may have been caused by loud noise according to a report from 2010 by the Centers for Disease Control and Prevention (CDC).
Causes of NIHL
NIHL can be caused by a one-time exposure to an intense impulse sound such as an explosion, or through continuous exposure to loud sounds over a long period of time, such as noise generated in a steel mill. Recreational activities that may place a person at risk for NIHL include:
- Playing in a band
- Snowmobile riding
- Attending loud concerts
- Listening to MP3 players at high volume through earbuds/headphones
Harmful noises at home might come from sources such as leaf blowers, lawnmowers and the use of power tools.
Sound is measured in units called, 'decibels.' Sounds of less than seventy-five decibels - even following long exposure, are not likely to cause hearing loss. Long or repeated exposure to sounds at or above eighty-five decibels; however, might cause hearing loss. The louder the sound, the shorter period of time it takes for a person to experience NIHL. What follows are the average decibel ratings of sounds that are familiar:
- Sirens, 120 decibels
- Motorcycles, 95 decibels
- Heavy traffic noise, 85 decibels
- Average conversation, 60 decibels
- A humming refrigerator, 45 decibels
- Firearms or firecrackers, 150 decibels
- An MP3 player at maximum volume, 105 decibels
A person's distance from the source of the sound, as well as the length of time they are exposed to the sound, are also important factors in protecting their hearing. A good rule is to avoid noises that are too close, too loud, or which last too long.
How Noise Can Damage Your Hearing
In order to understand how loud noises may damage a person's hearing, we need to understand how people hear. Hearing depends on a series of events that change sound waves in the air into electrical signals. Our auditory nerve then carries these signals to the person's brain via a complex series of steps which include:
- Sound waves enter the person's outer ear and travel through a narrow passage called the ear canal, which leads to the person's eardrum.
- The person's eardrum vibrates from incoming sound waves and sends the vibrations to three tiny bones in the person's middle ear; the bones are called the incus, malleus and stapes.
- The bones in the person's middle ear couple the sound vibrations from the air to fluid vibrations in their cochlea in their inner ear, which is shaped like a snail and filled with fluid. An elastic partition runs from the start to the end of the cochlea, splitting it into a lower and upper part. The partition is called the, 'basilar membrane,' because it serves as the base on which key hearing structures sit.
- After the vibrations cause the fluid inside the person's cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells; sensory cells sitting on top of the basilar membrane, ride the wave.
- As the hair cells move up and down, microscopic hair-like projections known as, 'stereocilia,' that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When this occurs, chemicals rush into the cell creating an electrical signal.
- The auditory nerve carries the electrical signal to the person's brain, which then translates it into a sound that the person can recognize and understand.
The majority of NIHL is caused by the damage and eventual death of these hair cells. Unlike amphibian and bird hair cells - human hair cells do not grow back; they are gone for good.
Effects and Signs of NIHL
When a person is exposed to loud noise over an extended period of time, they might slowly begin to lose their hearing. Due to the damage from noise exposure being gradual the person may not notice it, or they may ignore the signs of hearing loss until they become more pronounced. Over a period of time, sounds might become muffled or distorted and the affected person may find it hard to understand what others are saying when they speak, or have to turn up the volume on their television. The damage from NIHL - in combination with the person's age, may lead to hearing loss severe enough that the person needs hearing aids to magnify the sounds around them and help them hear, communicate and participate more fully in everyday activities.
NIHL may also be caused by very loud bursts of sound, such as explosions or gunfire, which can rupture the person's eardrum or damage the bones in the person's middle ear. This kind of NIHL may be immediate and permanent. Exposure to loud noise may also cause tinnitus, which is a buzzing, ringing or roaring in the person's ears or head. Tinnitus may subside over time, although it may at times continue occasionally or constantly throughout the person's lifetime. Hearing loss and tinnitus can happen in one or both of a person's ears.
Sometimes, exposure to impulse or continuous loud noises causes a temporary hearing loss that disappears sixteen to forty-eight hours later. Recent research suggests; however, that even though the loss of hearing seems to disappear, there might be residual long-term damage to a person's hearing.
NIHL is the only type of hearing loss that is entirely preventable. If people understand the hazards of noise and how to practice good hearing health, they can protect their hearing for life; here is how:
- Be alert to hazardous noises in the environment
- Know which noises may cause damage or noise above 85 decibels
- Have your hearing tested if you believe you may have hearing loss
- Protect the ears of children who are too young to protect their own
- Wear earplugs or other protective devices when involved in loud activities
- Make family members, friends and colleagues aware of the hazards of noise
- If you cannot reduce the noise or protect yourself from it - move away from it
- 1 - Auditory Processing Disorder (APD) | Deafness Research UK | 2010/02/04
- 2 - Restoring Hearing for Millions of Elderly and Others with Hearing Loss | University of Southern California | 2018/04/05
- 3 - Synesthesia: Search for Genes with Ability to See Sounds | Cell Press | 2009/02/05
- 4 - Deaf Children and Cognitive Development | University of Connecticut | 2016/02/13
- 5 - Misophonia and Sensory Processing Disorder | Thomas C. Weiss | 2013/07/29
- 6 - Sustaining a Career After Acquired Hearing Loss | Oregon State University | 2017/02/22
- 7 - Harder to Hear in Noisy Environments for Hearing Impaired | Purdue Department of Speech, Language and Hearing Sciences | 2012/09/11
- 8 - Second Cause of Hidden Hearing Loss Identified | Michigan Medicine - University of Michigan | 2017/02/18