Sensorineural hearing loss happens when the delicate sensory cells inside your inner ear, or the nerve pathways connecting them to your brain, become damaged. It is the most common type of permanent hearing loss, affecting over 430 million people worldwide at a disabling level. The causes range from prolonged noise exposure and aging to genetics, infections, certain medications, and sudden unexplained events.
How the Inner Ear Gets Damaged
Deep inside your ear sits the cochlea, a snail-shaped structure lined with thousands of tiny sensory hair cells. These cells convert sound vibrations into electrical signals that travel along the auditory nerve to your brain. Unlike skin or bone cells, hair cells in the human ear do not regenerate. Once they’re destroyed, the hearing they supported is gone permanently.
Hair cells can be damaged in several ways. Intense sound, toxic chemicals, or simply years of use can break the microscopic filaments (called tip links) that sit on top of each cell and detect vibration. Milder damage may disrupt how the cell processes sound without killing it outright, leading to distorted hearing rather than total silence in certain frequencies. More severe stress triggers the cell to self-destruct through a process driven largely by reactive oxygen species, unstable molecules that overwhelm the cell’s defenses and cause irreversible damage to its internal structures, particularly the mitochondria that power it.
Even when hair cells survive, the synapses connecting them to auditory nerve fibers can degrade. This “hidden” damage doesn’t always show up on a standard hearing test, but it makes it harder to understand speech in noisy environments. It’s one reason two people with similar audiogram results can have very different real-world hearing ability.
Noise Exposure
Noise is one of the most preventable causes of sensorineural hearing loss. Sounds at or below 70 decibels, roughly the volume of a washing machine, are unlikely to cause damage even after long exposure. But repeated or prolonged exposure at 85 decibels or above (think heavy traffic, a crowded restaurant, or a lawnmower) can permanently destroy hair cells. The louder the sound, the less time it takes: a rock concert at 110 decibels can cause damage in under five minutes.
Noise damage is cumulative. A single loud event can cause immediate, noticeable hearing loss, but more often the damage builds over years of moderate overexposure. Construction workers, musicians, military personnel, and anyone who regularly uses earbuds at high volume are at elevated risk. Because the loss develops gradually, many people don’t realize it’s happening until it’s significant.
Aging
Age-related hearing loss, called presbycusis, is the most common form of sensorineural hearing loss in adults. Between 30 and 35 percent of adults aged 65 to 75 have measurable hearing loss, and that figure rises to 40 to 50 percent for people over 75. The World Health Organization projects that by 2050, one in ten people globally will have disabling hearing loss, driven largely by aging populations.
Presbycusis typically starts with the high-frequency hair cells at the base of the cochlea, which is why older adults often lose the ability to hear consonant sounds like “s,” “f,” and “th” before they notice trouble with lower-pitched vowels. Years of accumulated oxidative stress, reduced blood flow to the cochlea, and gradual stiffening of inner ear structures all contribute. Genetics, noise history, cardiovascular health, and diabetes can all accelerate the timeline.
Genetic Causes
Genetics account for a large share of hearing loss present at birth. Variants in the GJB2 gene are among the most common genetic causes of hearing loss worldwide and are the leading genetic cause of severe-to-profound sensorineural hearing loss in newborns across many populations. The GJB2 gene provides instructions for making a protein called connexin 26, which helps maintain the chemical balance inside the cochlea that hair cells need to function. When both copies of the gene carry a mutation (inherited from each parent), the cochlea can’t regulate itself properly, and hearing loss is typically present from birth.
More than 100 other genes have been linked to nonsyndromic hearing loss (hearing loss that occurs without other medical features). Some genetic forms are progressive, meaning a child is born with normal hearing that deteriorates over months or years. Syndromic forms, where hearing loss accompanies other symptoms like vision problems or heart conditions, account for about 30 percent of genetic cases.
Ototoxic Medications
Certain medications are directly toxic to the hair cells or auditory nerve fibers. The best-documented culprits fall into a few major drug classes:
- Aminoglycoside antibiotics (such as gentamicin, tobramycin, and amikacin) are powerful drugs used for serious bacterial infections. Depending on the specific drug and dosing, up to 33 percent of adult patients show measurable hearing changes during treatment. In parts of the world where these antibiotics are used more freely, they cause as many as 66 percent of cases of profound childhood hearing loss.
- Platinum-based chemotherapy drugs used in cancer treatment are well known for causing high-frequency hearing loss that can be permanent. The risk increases with higher cumulative doses.
- Loop diuretics, prescribed for heart failure and severe fluid retention, can cause temporary or permanent hearing loss, especially at high intravenous doses or when combined with other ototoxic drugs.
- High-dose aspirin and quinine can cause reversible hearing loss and ringing in the ears. Symptoms typically resolve once the medication is stopped or the dose is reduced.
The risk from these drugs is higher when two or more ototoxic medications are used together, or when kidney function is impaired (since slower drug clearance means longer exposure to the inner ear).
Infections
Several viral and bacterial infections can damage the cochlea or auditory nerve. Before widespread vaccination, mumps was the most common cause of acquired hearing loss in children in the United States. Wild-type mumps virus causes temporary high-frequency hearing loss in about 4.4 percent of cases and permanent unilateral deafness in roughly 1 in 20,000 cases, through direct viral infection of inner ear structures.
Measles can cause hearing loss as well, most often as a complication of the brain inflammation (encephalitis) it sometimes triggers. Bacterial meningitis is another significant cause. The infection can spread to the cochlea and, in severe cases, cause the fluid-filled chambers of the inner ear to calcify, leading to profound hearing loss that is difficult to treat even with cochlear implants. Congenital cytomegalovirus (CMV) infection, which often produces no visible symptoms in newborns, is the leading nongenetic cause of sensorineural hearing loss in children.
Sudden Sensorineural Hearing Loss
Sudden sensorineural hearing loss (SSHL) is defined as a drop of at least 30 decibels across three connected frequencies within 72 hours. It usually strikes one ear and is often noticed first thing in the morning or accompanied by a “pop.” Most cases are idiopathic, meaning no specific cause is identified despite thorough testing. Possible triggers include viral infections, blood flow disruptions to the cochlea, autoimmune reactions, and inner ear membrane ruptures.
SSHL is a medical urgency. Steroid treatment should begin as soon as possible for the best chance of recovery, and treatment delayed more than two to four weeks is significantly less likely to reverse or reduce permanent damage. About one-third of people with SSHL recover fully, another third recover partially, and the remainder experience lasting hearing loss. Because many people assume a plugged ear is just wax or congestion and wait too long, the condition is likely underdiagnosed.
Other Contributing Causes
Ménière’s disease causes episodes of vertigo, tinnitus, and fluctuating low-frequency hearing loss that can become permanent over time. The exact mechanism isn’t fully understood, but it involves abnormal fluid pressure in the inner ear. Autoimmune inner ear disease, where the body’s immune system attacks cochlear tissue, is a rare but treatable cause if caught early. Acoustic neuromas, benign tumors on the auditory nerve, can gradually compress nerve fibers and cause one-sided hearing loss.
Head trauma, particularly fractures of the temporal bone surrounding the ear, can damage the cochlea or sever auditory nerve connections directly. Chronic conditions like diabetes and cardiovascular disease also increase risk by reducing blood flow to the tiny vessels that supply the cochlea, starving hair cells of oxygen over time.
How Severity Is Classified
Hearing loss is measured in decibels on an audiogram, and the degree of loss determines what sounds you can and can’t detect. Mild loss (20 to 40 dB) means you miss soft sounds and may struggle to follow conversations in noisy settings. Moderate loss (41 to 55 dB) makes even some quiet conversations hard to hear. Profound loss (above 90 dB) means you generally cannot understand speech and may not hear loud everyday sounds like a lawnmower or a passing car. Most causes of sensorineural hearing loss affect high frequencies first, so the earliest sign is often difficulty understanding speech rather than an inability to hear sound at all.