The most common cause of sensorineural hearing loss worldwide is aging, a condition known as presbycusis. It affects roughly two-thirds of Americans aged 70 and older and accounts for more cases than all other causes combined. Noise exposure ranks as the second most common cause, followed by genetics, certain medications, and infections.
How Aging Damages Your Inner Ear
Sensorineural hearing loss happens when the tiny sensory cells inside the inner ear, called hair cells, become damaged or die. These cells convert sound vibrations into electrical signals your brain interprets as sound. You’re born with about 15,000 of them in each ear, and they don’t regenerate. Once they’re gone, that hearing is lost permanently.
With age, these hair cells gradually deteriorate. The internal support structures that keep them rigid slowly break down, and the cells lose their ability to respond to sound vibrations. This process typically begins with high-frequency sounds, which is why age-related hearing loss usually shows up first as difficulty understanding speech in noisy environments or trouble hearing consonants like “s,” “f,” and “th.” Over time, the loss spreads to lower frequencies. The progression is usually gradual enough that many people don’t notice it for years.
Age-related hearing loss isn’t purely about the ear itself. The auditory nerve, which carries signals from the hair cells to the brain, also degrades over time. Blood flow to the inner ear decreases with age, and the cumulative effects of a lifetime of noise exposure, medications, and other stressors compound the damage. Among people older than 60, over 25% have disabling hearing loss according to the World Health Organization.
Noise Exposure: The Leading Preventable Cause
While aging is the most common cause overall, noise-induced hearing loss is the most common preventable cause. Sounds at or below 70 decibels, about the level of a washing machine, are unlikely to cause damage even after prolonged exposure. But repeated or sustained exposure to sounds at or above 85 decibels (heavy city traffic, a lawnmower, a crowded restaurant) can destroy hair cells permanently. The louder the sound, the less time it takes to cause damage.
This isn’t just a workplace hazard. CDC data shows that one in every six to eight U.S. adolescents aged 12 to 19 already has measurable hearing loss likely caused by excessive noise exposure. About three in four teenage students reported being exposed to loud sounds at school, and nearly half said that exposure was regular. Personal listening devices, concerts, sporting events, and even school environments all contribute.
The cellular damage from noise is similar to what happens with aging, just accelerated. Intense sound overstimulates the hair cells, causing their internal protein scaffolding to break apart. Mild damage can sometimes repair itself if the ear gets enough quiet recovery time. But severe or repeated exposure causes the structural supports to fuse together or develop holes, leading to permanent cell death.
Genetic Causes
Genetics are the most common cause of sensorineural hearing loss present at birth. Mutations in a gene called GJB2 are responsible for the majority of inherited cases across many world populations. This gene provides instructions for building proteins that help cells in the inner ear communicate with each other. When both copies of the gene carry a mutation, the result is typically severe-to-profound hearing loss that doesn’t worsen over time.
Carrier rates vary by population. The highest reported carrier rate is 8.3% in East Asian populations. Most people who carry one copy of the mutation have normal hearing, but when two carriers have a child together, there’s a chance the child will inherit both copies. Genetic testing can identify these mutations, and it’s now a standard part of evaluating hearing loss in newborns.
Medications That Can Cause Hearing Loss
More than 200 medications are considered potentially toxic to the inner ear. The most commonly implicated groups are certain antibiotics used for serious bacterial infections and platinum-based chemotherapy drugs used to treat cancer. Both can damage or kill hair cells directly. Water pills (loop diuretics), which help the body shed excess fluid, can also cause hearing damage, though this is often reversible when the medication is stopped.
Even aspirin, taken in high doses over time, can cause temporary hearing changes or ringing in the ears. Environmental chemicals like mercury, lead, and carbon monoxide can also damage the inner ear. The risk from medications generally increases with higher doses, longer treatment courses, and when multiple ear-toxic drugs are used together.
Sudden Sensorineural Hearing Loss
Sensorineural hearing loss usually develops gradually, but it can also strike without warning. Sudden sensorineural hearing loss typically affects one ear and develops over hours to days. Only about 10% of people diagnosed with it ever learn the specific cause. When a cause is identified, it’s usually an infection, head trauma, an autoimmune disease, a blood circulation problem, or a disorder of the inner ear like Ménière’s disease.
Researchers suspect that disrupted blood flow to the inner ear or inflammation may explain many of the cases with no identified trigger. Sudden hearing loss is treated as a medical urgency because early treatment improves the chances of recovery.
How Sensorineural Loss Is Identified
A hearing test called an audiogram distinguishes sensorineural hearing loss from other types. The test measures how well you hear sounds delivered two ways: through the air (via headphones) and through bone (via a vibrating device placed behind your ear). Sound traveling through air passes through the outer ear, eardrum, and middle ear bones before reaching the inner ear. Sound delivered through bone bypasses all of that and stimulates the inner ear directly.
In sensorineural hearing loss, both pathways show the same degree of loss, with no significant gap between them (less than 10 decibels). This tells the clinician the problem is in the inner ear or auditory nerve, not in the eardrum or middle ear bones. If there’s a gap between air and bone conduction, the hearing loss is conductive, meaning something is blocking or dampening sound before it reaches the inner ear. Some people have a mix of both types.
The Scale of the Problem
Hearing loss is one of the most common chronic health conditions globally. The World Health Organization estimates that 430 million people currently need rehabilitation for disabling hearing loss, including 34 million children. By 2050, nearly 2.5 billion people are projected to have some degree of hearing loss, and over 700 million will need hearing rehabilitation. Nearly 80% of people with disabling hearing loss live in low- and middle-income countries, where access to hearing aids and audiological services is limited.
Among children specifically, about 95 million kids aged 5 to 19 live with hearing loss worldwide. Given the rising prevalence of noise-induced damage in adolescents, these numbers are expected to grow. The simplest protective measures, lowering the volume on audio devices, moving away from loud sound sources, and wearing earplugs in noisy settings, remain the most effective tools for preventing the second most common cause of sensorineural hearing loss.