Sensorineural deafness happens when the delicate structures of the inner ear or the nerve that carries sound signals to the brain become damaged. Unlike conductive hearing loss, which involves blockages or problems in the outer or middle ear, sensorineural loss is usually permanent. A wide range of conditions can cause it, from loud noise and aging to infections, medications, genetics, and tumors.
Noise Exposure
Prolonged or intense noise is one of the most common preventable causes. Sounds at or below 70 decibels, roughly the level of a washing machine, are unlikely to cause damage even after long exposure. But repeated exposure at or above 85 decibels (think heavy city traffic or a loud restaurant) can destroy the hair cells inside the cochlea that convert sound waves into electrical signals. The louder the sound, the less time it takes. A single gunshot or explosion can cause immediate, permanent loss.
Once those hair cells die, they don’t regenerate in humans. The damage is cumulative, so years of moderately loud occupational noise can be just as devastating as a single acoustic trauma.
Age-Related Hearing Loss
Presbycusis, the gradual hearing loss that comes with aging, is the single most common form of sensorineural deafness. Several things break down simultaneously in the aging ear. The stria vascularis, a tissue that maintains the chemical environment the hair cells need to function, shrinks. Hair cells themselves degenerate. Auditory nerve fibers deteriorate, particularly the low-spontaneous-rate fibers that help you hear in noisy environments. Blood vessels in the cochlea merge, slow down, and develop thickened walls, reducing oxygen and nutrient delivery.
The result is typically a slow, progressive loss of high-frequency hearing that makes speech harder to follow, especially in background noise. Stem cells in the inner ear lose their regenerative capacity with age, so the damage compounds over decades.
Ototoxic Medications
Certain drugs directly poison inner ear hair cells. The most well-known culprits fall into a few categories:
- Aminoglycoside antibiotics such as gentamicin, tobramycin, and amikacin. These are potent antibiotics used for serious infections, and they carry a significant risk of permanent hair cell destruction.
- Platinum-based chemotherapy drugs, particularly cisplatin, carboplatin, and oxaliplatin. Hearing loss is a recognized side effect of these cancer treatments.
- Loop diuretics used for heart failure and fluid retention.
- Antimalarials like quinine and chloroquine.
- High-dose aspirin and other NSAIDs, which can cause hearing changes that are sometimes reversible when the drug is stopped.
The risk increases when these drugs are combined. A patient receiving both an aminoglycoside antibiotic and a loop diuretic, for example, faces a higher chance of inner ear damage than with either drug alone.
Infections
Several viruses and bacteria can invade the inner ear and destroy its structures. Cytomegalovirus (CMV) is the leading infectious cause of sensorineural hearing loss in newborns. Temporal bone studies show the virus causes inflammation throughout the cochlea and spiral ganglion. Rubella directly kills cells in the organ of Corti and the stria vascularis, which is why vaccination programs have dramatically reduced deafness rates in countries where rubella is well controlled.
Measles causes degeneration of cochlear neurons and the organ of Corti. Mumps virus has been detected in the fluid-filled chambers of the inner ear itself. Herpes simplex virus can infiltrate cochlear nerve fibers. Bacterial meningitis remains a major cause of acquired deafness in children, as the infection can spread from the membranes surrounding the brain into the cochlea. Syphilis, particularly in its later stages, can also cause progressive sensorineural loss.
Genetic Causes
Roughly 50 to 60 percent of childhood hearing loss has a genetic origin. About 75 percent of genetic hearing loss is “non-syndromic,” meaning deafness is the only symptom with no other associated abnormalities. The remaining cases are syndromic, occurring alongside other conditions.
The most common genetic cause worldwide involves mutations in a gene called GJB2, which produces a protein called connexin 26. This protein forms tiny channels between cells in the inner ear that are essential for maintaining the chemical balance hair cells need to function. Mutations in this single gene are estimated to account for roughly half of all hereditary deafness. In European populations, one specific mutation (called 35delG) dominates, while different mutations in the same gene are more common in East Asian populations and among Ashkenazi Jewish families. Most of these cases follow a recessive inheritance pattern, meaning a child must inherit a faulty copy from both parents.
Acoustic Neuromas
An acoustic neuroma is a slow-growing, noncancerous tumor that develops on the vestibulocochlear nerve, the nerve that carries both hearing and balance information from the inner ear to the brain. Hearing loss is the most common and usually the earliest symptom. As the tumor grows, it compresses auditory nerve fibers or disrupts blood supply to the nerve, causing a slowly progressive, high-frequency sensorineural hearing loss that is almost always one-sided.
Because the loss develops gradually and only affects one ear, it can go unnoticed for months or years. Unexplained hearing loss in just one ear is one of the key red flags that prompts further investigation with imaging.
Autoimmune Inner Ear Disease
In autoimmune inner ear disease (AIED), the body’s immune system mistakenly attacks the inner ear. This triggers a combination of damaging processes: inflammation of cochlear blood vessels, formation of tiny blood clots, degeneration of the spiral ganglion (the cluster of nerve cells that relay sound), and atrophy of the organ of Corti where hair cells sit. The result is hearing loss that typically fluctuates and worsens over weeks to months, often affecting both ears.
AIED can occur on its own or alongside other autoimmune conditions. It is one of the few forms of sensorineural hearing loss that may partially respond to treatment aimed at suppressing the immune response, particularly when caught early.
Sudden Sensorineural Hearing Loss
Sudden sensorineural hearing loss (SSHL) is defined as a drop of 30 decibels or more across at least three connected sound frequencies, occurring within 72 hours. Most people notice it when they wake up or when they try to use the affected ear on a phone call. It almost always strikes one ear.
In most cases, no clear cause is identified. Proposed triggers include viral infections, disrupted blood flow to the cochlea, and immune-mediated inflammation. Roughly one-third to two-thirds of people recover some hearing spontaneously, but early treatment improves the odds. SSHL is considered a medical emergency because delays in care reduce the chance of recovery.
How Sensorineural Hearing Loss Is Managed
Because the inner ear damage behind sensorineural deafness is usually irreversible, management centers on amplification and rehabilitation. Hearing aids work well for mild to moderate loss by making sounds louder and clearer. For more severe cases, when a person understands fewer than 50 percent of words even with hearing aids, cochlear implants become an option. These devices bypass damaged hair cells entirely and stimulate the auditory nerve directly with electrical signals.
Preventing further damage matters too. Avoiding excessive noise, monitoring hearing during treatment with ototoxic drugs, and vaccinating against preventable infections like measles, mumps, and rubella are all practical steps that reduce risk. For genetic causes, carrier screening and newborn hearing tests allow early identification, which makes a significant difference in language development when intervention starts in the first months of life.