Diseases & Conditions

Acoustic Trauma - Occupational Hearing Loss

Overview, Causes, & Risk Factors

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:

  • harmful gases, such as carbon monoxide
  • heat
  • a loud, intense burst of sound, such as a gunshot
  • loud noise over a long period of time
  • metals, such as lead, arsenic, manganese, and mercury
  • solvents, such as toluene and other chemicals used in manufacturing
  • Individuals who are exposed to noise along with one of the other environmental factors may experience more significant hearing loss.