Perhaps the most common cause of injury to the cochlea is exposure to loud noise. This may be sudden, such as the sound of an explosion, or continuous, such as the ongoing noise encountered by heavy equipment operators, airport personnel, machine shop workers or soldiers deployed to battle zones. It is important for the ears to be protected when one is working in such an environment. Noise-related damage can also result from frequent exposure to loud music. An understanding of how sounds are detected makes it easier to understand how noise-related injuries occur.
The cochlea, located in the inner ear, is the main organ of hearing. It is coiled into a spiral shape and lined with hair cells. These are covered with tiny hair-like structures called cilia.
Sound waves entering the ear cause the cilia to sway back and forth, much as sea grass sways with the changing ocean currents. This movement sends signals to the brain via the auditory nerve, which interprets the signals as sound. The cilia can be easily damaged, which may cause the hair cells to die. The result is hearing loss or ringing in the ear that cannot be reversed.
Normal aging can bring about gradual, partial hearing loss. This results from accumulated wear and tear on the cilia, which can become inefficient over time. In later years, high-pitched sounds may become difficult to hear, and speech can become difficult to understand. Bent or broken cilia might begin to trigger random signals, which the brain interprets as sound. This results in tinnitus, which is a ringing or roaring in the ears.
A large number of illnesses can lead to hearing loss, especially if associated with high fevers. Many childhood diseases, such as measles, mumps and chickenpox, can permanently damage the inner ear. Vaccination of young children prevents most occurrences of these diseases.
Bacterial meningitis poses a severe risk of cochlear damage, as does mononucleosis. Hearing loss in young children might not be immediately apparent; it might in fact go undiagnosed until long after onset. Premature birth, congenital syphilis and low blood oxygen are all associated with increased risk of permanent damage to the inner ear in infants.
Other health problems might bring about hearing loss, as well. Untreated high blood pressure or cardiovascular disease, for example, can compromise blood flow to the inner ear, resulting in cochlear damage. Tumors of the inner ear, which are common in patients with acquired immunodeficiency syndrome (AIDS), pose a clear risk for cochlear damage.
Finally, the cochlea can be injured by certain drug regimens as well. For example, high doses of aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) can be associated with acute cochlear damage. Other commonly used medications sometimes associated with hearing loss include antibiotics, antihistamines, anti-convulsants, anti-depressants and anti-psychotics.
The inner ear is subject to injury from a wide array of potential insults. These are not limited to loud noises but include many common illnesses, health conditions and medications. It is impossible to predict what might prove dangerous for a specific individual. For this reason, changes in hearing should always be reported to a healthcare professional.