Noise-Induced Hearing Loss - Occupational Hearing Loss

Occupational hearing loss is a condition caused by environmental factors that damage structures involved in hearing. These structures include the ear, nerves, and brain.

What is going on in the body?

Sounds cause the eardrum to vibrate. Small bones transmit the vibration to the inner ear, which is filled with fluid. A bone in the inner ear called the stapes moves and creates a fluid wave. Hair cells in the snail-shell shaped cochlea in the inner ear detect these waves and convert them into nerve signals. These nerve signals are transmitted to the auditory nerve. The auditory nerve sends the signal into the brain, where it is interpreted as sound.

The snail-shell shape of the cochlea is arranged by pitch. At the top of the snail shell, low-frequency sounds are picked up. In the bottom turn of the snail shell, high pitches are detected. There are about 25,000 rows of hair cells, and each row responds to a particular pitch.

The hair cells can be damaged by loud noises. These noises may be consistently loud, such as at a rock concert, or very brief, such as sound from an explosion. Acute noise injury can cause both temporary and permanent damage. Over time, loud sounds can cause permanent injury because hair cells are lost. As hair cells are lost, the person becomes unable to hear sounds at those frequencies. The high-frequency first turn of the cochlea is the most easily injured area of the inner ear.

What are the causes and risks of the condition?

Most cases of occupational hearing loss develop gradually. Common environmental factors that contribute to hearing loss include the following:

Individuals who are exposed to noise along with one of the other environmental factors may experience more significant hearing loss.

What are the signs and symptoms of the condition?

The person with occupational hearing loss may have a feeling of fullness in the ears. Sounds may seem muffled. He or she cannot hear very well, especially at high frequencies. There is usually a high-frequency ringing in the ears.

Most people recover their hearing completely within 24 to 48 hours. However, even when hearing returns, hair cells are permanently damaged. People who are exposed to noise repeatedly over a long time will have those noise injuries build up. The result is a hearing loss at high frequencies that slowly gets worse. These people may not even be aware that anything is wrong with their hearing.

Some sounds are so loud that high-frequency hearing is immediately and permanently lost. Examples include explosions, artillery fire, fireworks, and gunshots. Some people seem to be more prone to injury from noise exposure. The same noise that causes hearing loss in them may present no difficulty for others. Hearing that does not return after an acute noise injury is called a permanent threshold shift.

How is the condition diagnosed?

Diagnosis of occupational hearing loss begins with a medical history and physical exam. The healthcare provider may order the following tests:

What can be done to prevent the condition?

The Occupational Safety and Health Administration, also called OSHA, sets limits on occupational noise exposure. People exposed to 85 decibels or more at work are required to wear some form of hearing protection. Ear protection should be worn whenever lawn mowers, string trimmers, or other loud equipment is used. The use of power woodworking tools in an enclosed space should be avoided.

People who abuse their own hearing, by listening to music that is too loud, for example, are risking permanent high-frequency hearing loss. The average age of people who get hearing aids is dropping. This means that people are being exposed to too much noise earlier in life.

People who work around loud noise should have regular hearing tests. If people do have hearing loss, they should be very careful to protect their remaining hearing. There are a number of devices that help to protect the ear from noise. Silicone putty and foam earplugs reduce noise by 20% to 25%. The best hearing protection is the combination of acoustic earmuffs and earplugs. Using this combination can reduce noise by 30 to 35 decibels.

What are the long-term effects of the condition?

The main long-term effect of noise exposure is high-frequency hearing loss. The loss keeps getting worse and cannot be reversed. People with this loss often have ringing of the ears, called tinnitus. They may also have trouble hearing conversation over background noise.

What are the risks to others?

Occupational hearing loss is not contagious and poses no risks to others.

What are the treatments for the condition?

Treatments for occupational hearing loss include the following:

What are the side effects of the treatments?

There are no side effects from the treatment options listed.

What happens after treatment for the condition?

Many people with hearing aids have a hard time communicating when there is a lot of background noise. Other people should be encouraged to speak into the less-impaired ear of the person. Gestures and facial expressions can also help, when used appropriately. The person may need assistance dealing with adjustment to hearing loss. He or she may have emotional reactions such as anger, frustration, and loneliness.

How is the condition monitored?

The healthcare provider may order periodic hearing tests to detect further hearing loss. Any new or worsening symptoms should be reported to the healthcare provider.

Author:Mark Loury, MD
Date Written:
Editor:Ballenberg, Sally, BS
Edit Date:07/31/01
Reviewer:Barbara Mallari, RN, BSN, PHN
Date Reviewed:06/26/01