What is noise-induced
hearing loss?
Every day, we experience sound in our
environment, such as the sounds from television and radio, household appliances, and traffic. Normally, we hear these sounds at safe levels that do not affect our
hearing. However, when we are exposed to harmful noise—sounds that are too loud or loud sounds that last a long time—sensitive structures in our inner ear can be damaged, causing noise-induced hearing loss (NIHL). These sensitive structures, called hair cells, are small sensory cells in the inner ear that convert sound energy into electrical signals that travel to the brain. Once damaged, our hair cells cannot grow back.
What sounds cause NIHL?
NIHL can be caused by a one-time exposure to an intense “impulse” sound, such as an explosion, or by continuous exposure to loud sounds over an extended period of time, such as noise generated in a woodworking shop. The loudness of sound is measured in units called decibels. For example, the humming of a refrigerator is 40 decibels, normal conversation is approximately 60 decibels, and city traffic noise can be 85 decibels. Sources of noise that can cause NIHL include motorcycles, firecrackers, and small firearms, all emitting sounds from 120 to 150 decibels.
What are the effects of NIHL?
Exposure to harmful sounds causes damage to the hair cells as well as the auditory, or hearing, nerve. Impulse sound can result in immediate hearing loss that may be permanent. This kind of hearing loss may be accompanied by tinnitus—a ringing, buzzing, or roaring in the ears or head—which may subside over time. Hearing loss and tinnitus may be experienced in one or both ears, and tinnitus may continue constantly or occasionally throughout a lifetime. Continuous exposure to loud noise also can damage the structure of hair cells, resulting in hearing loss and tinnitus, although the process occurs more gradually than for impulse noise.
Who is affected by NIHL?
People of all ages, including children, teens, young adults, and older people, can develop NIHL. Approximately ten percent of Americans between ages 20 and 69—or 22 million. Exposure occurs in the workplace, in recreational settings, and at home. Recreational activities that can put someone at risk for NIHL include target shooting and hunting, snowmobile riding, woodworking and other hobbies, playing in a band, and attending rock concerts.
Can NIHL be prevented?
NIHL is 100 percent preventable. All individuals should understand the hazards of noise and how to practice good hearing health in everyday life. To protect your hearing:
Know which noises can cause damage (those at or above 85 decibels).
Wear earplugs or other hearing protective devices when involved in a loud activity (special earplugs and earmuffs are available at hardware and sporting goods stores).
Be alert to hazardous noise in the environment.
Protect the ears of children who are too young to protect their own.
Make family, friends, and colleagues aware of the hazards of noise.
If you suspect hearing loss, have a medical examination by an otolaryngologist (a physician who specializes in diseases of the ears, nose, throat, head, and neck) and a hearing test by an audiologist (a health professional trained to measure and help individuals deal with hearing loss).
How We Hear
Hearing depends on a series of events that change sound waves in the air into electrical signals that the auditory nerve carries to the brain.
Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
The bones in the middle ear amplify, or increase, the sound and send the vibrations to the snail-shaped cochlea, or inner ear. The cochlea is a fluid-filled organ with an elastic
membrane that runs down its length and divides the cochlea into an upper and lower part. This membrane is called the “basilar” membrane because it serves as the base, or ground floor, on which key hearing structures sit.
The vibrations cause the fluid inside the cochlea to ripple, and a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the membrane—“ride the wave.” This motion causes bristly structures on top of the hair cells to bump up against an overlying membrane and deflect to one side.
As the bristles, or stereocilia, move, pore-like channels on their surface open up. This allows certain chemicals to rush in that generate an electrical signal.
The auditory nerve carries the signal to the brain, which translates it into a “sound” that we recognize and understand.
Hair cells near the base of the cochlea detect higher-pitched sounds, such as a cell phone ringing. Those nearer the apex, or centermost point, detect lower-pitched sounds, such as a large dog barking.