About Hearing Loss

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How Hearing Loss Occurs

Hearing loss can result from damage to structures or nerve fibers in the inner ear that respond to sound. This type of hearing loss, termed “noise-induced hearing loss,” is usually caused by exposure to excessively loud sounds and cannot be medically or surgically corrected.1

Sound intensity is measured in decibels with a sound level meter. Noise-induced hearing loss can result from a one-time exposure to a very loud sound (at or above 120 decibels), blast, impulse, or by listening to loud sounds (at or above 85 decibels) over an extended period. The louder the sound, the shorter the time period before hearing damage occurs.2

Signs and Symptoms of Hearing Loss

Because the damage from noise exposure is usually gradual, a person might not notice or might ignore signs of hearing loss until more pronounced symptoms of permanent hearing loss become evident.3 Noticeable signs of hearing loss can include the following2:

  • Muffled or distorted hearing
  • Difficulty hearing sounds such as birds singing, crickets chirping, alarm clocks, watch alarms, telephones, or doorbells
  • Difficulty understanding speech during telephone conversations or while participating in group conversations
  • Pain or ringing in the ears (tinnitus) after exposure to excessively loud sounds

If a child or adolescent experiences any of these signs, he or she should tell a parent, teacher, or other trusted adult. Often, family members, coworkers, or friends are the first to notice hearing problems in others. The only accurate way to determine the extent and degree of hearing loss is through evaluation by an expert trained to test hearing (audiologist) or other qualified professional.2

How Much Noise Is Too Much?

Noise exposures add up throughout daily activities. However, certain events, behaviors, and environmental factors in and out of the school setting can expose young people to unsafe sound levels:

  • Exposure to sound levels that exceed safe listening levels, such as at rock concerts or band practice, can cause hearing damage if it occurs frequently or for long periods of time.4
  • Listening to portable media devices such as compact disc and MP3 players at high volume levels (above 85 decibels) for long periods of time can cause similar damage.5
  • In the school setting, children and adolescents can be exposed to sounds that can damage their hearing, such as in band or shop class or attending school events (dances, athletic events) with excessive sound levels.
  • Construction and maintenance activities in or around the school can also expose students to harmful sound levels.

Based on the recommended exposure limits identified in the National Institute for Occupational Safety and Health (NIOSH) Revised Criteria for a Recommended Standard: Occupational Noise Exposure, the table below provides some common sound sources, their corresponding sound intensities (in decibels), and the duration of exposure limits before hearing damage begins.
 

Table 1: Sound, Sound Intensity, and Recommended Exposure Limits 

Safe Sound Level
Sound Source Examples
Sound Intensity (Decibels)
Recommended Exposure Limits For Repeated Exposures*
Comments
       
Quietest sound heard by person with normal healthy hearing 0 Any duration None
Quiet empty classroom that meets U.S. acoustical standard† 35–40 Any duration None
Typical library sound levels 40 Any duration None
Typical unoccupied classroom 46 Any duration None
Normal conversational speech 60 Any duration None
Battery-powered pencil sharpener 71 Any duration None

 

 

      
Potentially Hazardous Sound Level
Sound Source Examples
Sound Intensity (Decibels)
Recommended Exposure Limits For Repeated Exposures*
Comments
       
School cafeteria 85 8 hours Prolonged exposures might cause slight hearing loss. Hearing protection should be used if regularly exposed to this sound level beyond the exposure limit.‡
       
Band class 90 2 hours Hearing protection should be used if regularly exposed to this sound level beyond the exposure limit.‡
       
Wood or metal shop, power tools, snowmobile 100 15 minutes Hearing protection should be used if exposed to this sound level beyond the exposure limit.‡

 

 

      
Hazardous Sound Level
Sound Source Examples
Sound Intensity (Decibels)
Recommended Exposure Limits For Repeated Exposures*
Comments
       
Personal stereo system at high volume 105 5 minutes Hearing protection should be used if exposed to this sound level beyond the exposure limit.‡
       
Chainsaw, loud rock concert 110 1.5 minutes Hearing protection should be used if exposed to this sound level beyond the exposure limit.‡
       
Ambulance siren 120 9 seconds Hearing protection should be used if exposed to this sound level beyond the exposure limit.‡
       
Firecrackers, firearms 140-165 Immediate hearing
damage possible		 Hearing protection should be used whenever exposed to this sound level.‡

*NIOSH Recommended Exposure Limits (RELs) are based on repeated exposures occurring over a period of years. For example, repeated exposure to 85 decibels during an 8-hour workday over a period of years or repeated exposure to 90 decibels during a 2-hour period over a period of years are potentially hazardous. Hearing damage from noise adds up over time. Single, one-time exposures do not pose an immediate risk of hearing loss unless sound levels equal or exceed 140 decibels.

† American National Standards Institute (ANSI) S12.60 (2002).

‡ Hearing protection devices include earplugs and earmuffs that are made to reduce the loudness of sound. Earplugs are placed in the ear canal so that they totally block the canal, reducing the loudness of sound. Earmuffs fit completely over both ears, fitting tightly to reduce the sound loudness. It is recommended that earplugs and earmuffs be used together when noise exposure is particularly high. Cotton in the ears, winter ear warmers, and audio headphones are not appropriate hearing protection devices.6
References
  1. CDC/NIOSH. Noise and Hearing Loss Prevention. Cincinnati, OH: U.S. Department of Health and Human Services; 1998.
     
  2. National Institute on Deafness and Other Communication Disorders. Noise Induced Hearing Loss. Bethesda, MD: April 2007. NIH Pub No. 97-4233.
     
  3. Lass NJ, Woodford CM, Lundeen C, Lundeen DJ, Everly-Myers DS. The prevention of noise-induced hearing loss in the school-aged population: a school educational hearing conservation program. Journal of Auditory Research 1986;26:247–254.
     
  4. American Speech-Language-Hearing Association. Noise and Hearing Loss. Rockville, MD: American Speech-Language-Hearing Association.
     
  5. Fligor BJ, Cox LC. Output levels of commercially available portable compact disc players and the potential risk to hearing. Ear and Hearing 2004;25(6):513–527.
     
  6. CDC/NIOSH. What Does the Hearing Loss Program Do? Cincinnati, OH: U.S. Department of Health and Human Services.