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Noise Induced Hearing Loss

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What sounds cause NIHL?

NIHL can be caused by a one-time exposure to loud sound as well as by repeated exposure to sounds at various loudness levels over an extended period of time. The loudness of sound is measured in units called decibels. For example, normal conversation is approximately 60 decibels, the humming of a refrigerator is 40 decibels, and heavy city traffic noise can be 85 decibels. Examples of sources of loud noises that cause NIHL are motorcycles, firecrackers, and firearms, all emitting sounds from 120 to 150 decibels. Sounds of less than 80 decibels, even after long exposure, are unlikely to cause hearing loss.

Exposure to harmful sounds causes damage to the sensitive hair cells of the inner ear as well as the hearing nerve. These structures can be injured by two kinds of noise: loud impulse noise, such as an explosion, or loud continuous noise, such as that generated in a woodworking shop.


What are the effects of NIHL?

Impulse sound can result in immediate hearing loss that may be permanent. The structures of the inner ear may be severely damaged. 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 the hair cells, resulting in hearing loss and tinnitus. Exposure to impulse and continuous noise may cause only a temporary hearing loss. If the hearing recovers, 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.

Both forms of NIHL can be prevented by the regular use of hearing protectors such as earplugs or earmuffs.

What are the symptoms of NIHL?

The symptoms of NIHL increase gradually over a period of continuous exposure. Sounds may become distorted or muffled, and it may be difficult for the person to understand speech. The individual may not be aware of the loss, but it can be detected with a hearing test.

Can NIHL be prevented?

NIHL is preventable. All individuals should understand the hazards of noise and how to practice good health in everyday life.

• Know which noises can cause damage (those above 85 decibels).

• Wear earplugs or other hearing protective devices when involved in a loud activity (special earplugs and earmuffs are available at hardware stores and sporting good stores).

• Be alert to hazardous noise in the environment.

• Protect children who are too young to protect themselves.

• Make family, friends, and colleagues aware of the hazards of noise.

• 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 identify and measure hearing loss and to rehabilitate persons with hearing impairments.

Ten Ways To Recognize Hearing Loss

The following questions will help you determine if you need to have your hearing evaluated by a medical professional:

Do you have a problem hearing over the telephone?

Yes No

Do you have trouble following the conversation when two or more people are talking at the same time?

Yes No

Do people complain that you turn the TV volume up too high?

Yes No

Do you have to strain to understand conversation?

Yes No

Do you have trouble hearing in a noisy background?

Yes No

Do you find yourself asking people to repeat themselves?

Yes No

Do many people you talk to seem to mumble (or not speak clearly)?

Yes No

Do you misunderstand what others are saying and respond inappropriately?

Yes No

Do you have trouble understanding the speech of women and children?

Yes No

Do people get annoyed because you misunderstand what they say?

Yes No

If you answered "yes" to three or more of these questions, you may want to see an otolaryngologist (an ear, nose, and throat specialist) or an audiologist for a hearing evaluation.

The material on this page is for general information only and is not intended for diagnostic or treatment purposes. A doctor or other health care professional must be consulted for diagnostic information and advice regarding treatment.

Excerpt from NIH Publication No. 01-4913

For more information, contact the NIDCD Information Clearinghouse.

Although sound levels under 85 decibels are generally considered safe, some people may have hearing damage with prolonged exposure to noise levels of as little as 82 decibels. For example, sound levels from common lawn equipment, such as gas mowers, leaf blowers and chain saws range from 90 to 115 decibels. Other power tools, such as belt sanders and drills, can create noises volumes of 95 to 100 decibels. Football stadiums are filled with noises 90 to 110 decibels loud and city traffic can reach 100 decibels, according to the National Campaign for Hearing Health. (

These sound levels can producing hearing loss in a matter of hours with unprotected exposure. A combination of them increases the sound level to even more damaging levels.

Even safe sound levels can become potentially damaging when they occur simultaneously. Sound levels from household appliances such as vacuum cleaners, coffee grinders



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