Do you Wear Ear Plugs to Mow your Lawn? Do you Wear Ear Plugs to Mow your Lawn?
National Institute on Deafness and Other Communication Disorders

What is noise-induced hearing loss?


What sounds cause NIHL?



What are the effects of NIHL?
Exposure to harmful sounds causes damage to the hair cells as well as the auditory, or hearing, nerve (see figure). 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.

Exposure to impulse and continuous noise may cause only a temporary hearing loss. If a person regains hearing, the temporary hearing loss is called a temporary threshold shift. The temporary threshold shift largely disappears 16 to 48 hours after exposure to loud noise. You can prevent NIHL from both impulse and continuous noise by regularly using hearing protectors such as earplugs or earmuffs.

What are the symptoms of NIHL?

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 Americans—already may have suffered permanent damage to their hearing from excessive noise exposure. 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. Harmful noises at home may come from lawnmowers, leafblowers, and shop tools.

Can NIHL be prevented?

Be alert to hazardous noise in the environment.

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.

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.

What research about NIHL is being conducted?
The National Institute on Deafness and Other Communication Disorders (NIDCD) researches the causes, diagnosis, treatment, and prevention of hearing loss. Most hearing loss is caused by damaged hair cells, which do not grow back in humans and other mammals. NIDCD-supported researchers have helped to identify some of the many genes important for ear development and hearing. One gene has been found to regrow hair cells in guinea pigs. More important, the treated animals were able to regain some of their lost hearing. This experiment is the first successful demonstration of gene therapy that improves hearing in formerly deaf animals. Scientists hope to one day use this type of gene therapy to restore hearing in humans.

NIDCD researchers also are investigating a potential way to prevent NIHL after noise exposure. Noise exposure triggers the formation of destructive molecules, called free radicals, that cause hair cell death. Researchers initially had thought that antioxidants, chemicals that protect against cell damage from free radicals, might prevent NIHL only if the antioxidants were given before noise exposure. In a recent study, however, the antioxidants in salicylate (aspirin) and Trolox (vitamin E) were given to guinea pigs as long as three days after noise exposure and still significantly reduced hearing loss. These results suggest that there is a window of opportunity in which it is possible to rescue hearing from noise trauma. Scientists hope to begin clinical trials with humans with the goal of reducing NIHL.

Where can I get more information?
NIDCD maintains a directory of organizations that can answer questions and provide printed or electronic information on NIHL. Please see the list of organizations at