Tinnitus is the medical term for the perception of sound, such as ringing, buzzing, or hissing, when no external sound is present. This auditory sensation is the most common service-connected disability among U.S. veterans, affecting over 2 million former service members. The high prevalence of tinnitus in the military population highlights the severe acoustic and physical stresses encountered during service. Understanding the various causes is the first step in addressing this condition.
Hazardous Noise Environments
The primary factor driving tinnitus cases in the military is intense acoustic exposure. Military environments are characterized by two types of hazardous noise: impulse noise and continuous noise. Impulse noise consists of sudden, extremely high-level sounds, such as those produced by artillery fire, improvised explosive device (IED) detonations, and small arms fire. A single shot from many military weapon systems can exceed 140 decibels (dB), the maximum safe peak level for an unprotected ear, with some systems reaching over 180 dB at the operator’s position.
Continuous noise comes from military vehicles, aircraft, and machinery. Aircraft engines, armored personnel carriers, and shipboard engine rooms expose personnel to sustained noise levels often between 85 and 110 dBA. Exposure to noise at or above 85 dBA for an eight-hour period typically necessitates a hearing conservation program, yet military personnel often operate in environments that mandate remaining in this hazardous noise for extended periods. Standard hearing protection devices frequently fail to provide adequate attenuation against the extreme peak pressures of impulse noise, or they are not worn consistently due to the need for situational awareness and clear communication. This consistent overexposure to both sudden blasts and sustained loud machinery results in cumulative damage to the auditory system.
Traumatic Brain Injury and Other Factors
Beyond direct acoustic trauma, other factors specific to military operations contribute to the development of tinnitus, most notably Traumatic Brain Injury (TBI). Blast exposure, common in combat zones, can cause TBI even without a direct head impact, as the force of the pressure wave travels through the body and skull. TBI, even in its mild form, is strongly associated with the incidence of tinnitus, with studies finding a link in up to 75% of cases.
The connection between TBI and tinnitus suggests that the damage is not purely localized to the inner ear, but also involves the central nervous system. Blast-related TBI increases the risk of developing new-onset tinnitus, indicating a neurological pathway for the sound perception. The likelihood of tinnitus also increases if the service member experiences multiple TBIs or reports moderate to severe symptoms.
Certain medications, known as ototoxic drugs, can also contribute to or exacerbate tinnitus and hearing loss. These medications, such as some antibiotics (like aminoglycosides and macrolides), high-dose aspirin, and chemotherapy agents, are often used to treat serious conditions but can damage the sensory structures of the inner ear. The use of these medications, sometimes necessary in field medicine, can synergistically increase the risk of hearing loss and tinnitus when combined with the hazardous noise environment.
How Damage Leads to Tinnitus
The sensation of tinnitus begins with damage to the cochlea, the snail-shaped organ in the inner ear. The cochlea contains thousands of microscopic hair cells responsible for amplifying and fine-tuning sound vibrations before they are sent to the brain. Intense noise exposure, whether from a sudden blast or prolonged loud machinery, mechanically damages these hair cells, leading to their permanent loss.
When these hair cells are damaged, the auditory nerve fibers connecting the ear to the brain receive a reduced or distorted signal, sometimes called “hidden hearing loss.” The brain attempts to compensate for this lack of sensory input by increasing spontaneous neural activity in the central auditory pathways, particularly in the brainstem’s cochlear nucleus. This heightened, synchronized, and disorganized electrical activity is then interpreted by the brain as sound. This maladaptive process, often described as neural plasticity, means that tinnitus is a brain response to a damaged ear.