Hearing loss in one ear affects roughly 7% of American adults and has a wide range of causes, from something as simple as earwax buildup to conditions that need urgent medical attention. The underlying problem can sit anywhere along the path sound travels, from the ear canal through the middle ear bones to the inner ear’s nerve cells and even the brain itself. Pinpointing the cause matters because some of these conditions are fully reversible, while others require fast treatment to prevent permanent damage.
Earwax Blockage
The most common and most fixable cause is a buildup of earwax that completely blocks the ear canal. Because wax tends to accumulate unevenly, it often plugs one side while leaving the other clear. A full blockage can reduce hearing by 20 to 60 decibels depending on severity, enough to make normal conversation sound muffled or distant. This type of hearing loss is “conductive,” meaning sound vibrations are physically blocked before they reach the eardrum. Once the wax is removed, hearing returns to normal almost immediately.
Ear Infections and Fluid Buildup
Middle ear infections cause swelling and fluid accumulation behind the eardrum, dampening the vibration of the tiny bones that transmit sound. Because infections typically start on one side, this is a frequent reason for sudden one-sided hearing trouble, especially in children. The hearing loss usually resolves as the infection clears, though repeated infections can cause lasting damage.
Labyrinthitis, an infection or inflammation of the inner ear, is more serious. Unlike a standard middle ear infection, labyrinthitis affects the nerve structures responsible for both hearing and balance. The hearing loss it causes tends to be profound and is often accompanied by intense vertigo. A related condition, vestibular neuritis, causes similar dizziness but does not affect hearing because the inflammation targets balance nerves while leaving the hearing nerve intact.
Sudden Sensorineural Hearing Loss
Sometimes hearing in one ear drops sharply with no obvious explanation. Doctors define sudden sensorineural hearing loss (SSHL) as a drop of at least 30 decibels across three connected sound frequencies within 72 hours. People often notice it first thing in the morning or when they try to use a phone on the affected side. Some hear a loud pop before the loss begins.
The exact trigger is unknown in most cases. Viral infections, disrupted blood flow to the inner ear, and autoimmune reactions are leading theories. What is clear is that treatment timing matters. Corticosteroid therapy started within the first seven days gives the best odds of recovery, with more than half of the most severely affected patients regaining usable hearing when treated in that window. Waiting longer significantly reduces those chances, which is why any rapid hearing change in one ear warrants same-day medical attention.
Ménière’s Disease
Ménière’s disease is a chronic inner ear disorder that produces recurring episodes of vertigo, hearing loss, tinnitus, and a feeling of pressure or fullness in one ear. Episodes can last anywhere from 20 minutes to several hours and are often unpredictable. Some attacks involve vertigo so severe that people lose their balance and fall.
The hearing loss in Ménière’s disease tends to fluctuate early on, coming and going with episodes. Over time, though, hearing in the affected ear often declines permanently. The condition is thought to involve excess fluid in the inner ear, but exactly why this happens remains unclear. It almost always affects one ear, at least initially.
Acoustic Neuroma
An acoustic neuroma (also called vestibular schwannoma) is a benign tumor that grows on the nerve connecting the inner ear to the brain. About 9 out of 10 people with this tumor experience hearing loss on the affected side. The loss is usually gradual, worsening over months to years, though in rare cases it can be sudden.
Tinnitus in the affected ear is another hallmark, along with balance problems and sometimes facial numbness. Because the tumor grows slowly, symptoms can be subtle at first. Hearing loss that steadily worsens on one side, particularly when paired with persistent ringing, is the combination that most often leads to diagnosis.
Cholesteatoma
A cholesteatoma is an abnormal skin growth that develops in the middle ear, usually behind the eardrum. It often follows repeated ear infections or problems with the eustachian tube. The most noticeable symptom is a foul-smelling discharge from the ear, sometimes resembling pus. As the growth expands, it can erode the tiny bones that conduct sound, causing progressive hearing loss in that ear along with a sensation of pressure, dizziness, and recurring infections. Treatment is surgical, and the goal is to remove the growth before it damages surrounding structures permanently.
Head Trauma
A blow to the head can fracture the temporal bone, the section of skull that houses the ear structures. About 90% of temporal bone fractures spare the delicate inner ear capsule, though even these can disrupt the chain of tiny bones in the middle ear, blocking sound conduction. The remaining 10% of fractures crack through the inner ear itself, and the rate of permanent nerve-related hearing loss in those cases ranges from 40% to 100%. Sudden pressure changes from the impact can also tear the membrane separating the middle and inner ear, creating a leak of inner ear fluid that causes fluctuating hearing loss and dizziness.
Stroke and Vascular Events
One-sided hearing loss can, in rare cases, signal a stroke or disrupted blood flow in the brain. The hearing change typically comes on suddenly and is accompanied by vertigo, difficulty with balance, nausea, and vomiting. Other neurological symptoms like facial drooping, slurred speech, arm weakness, or vision changes are red flags that point toward a vascular emergency rather than a primary ear problem. This combination of symptoms calls for immediate emergency care.
Other Contributing Factors
Several additional conditions can produce hearing loss that is worse on one side or limited to one ear:
- Noise exposure. Prolonged or repeated exposure to loud sound on one side (operating machinery, shooting a firearm from a dominant hand) damages the hair cells of the inner ear asymmetrically.
- Otosclerosis. Abnormal bone growth around one of the middle ear bones can stiffen it in place, preventing it from vibrating properly. This condition sometimes affects both ears but often starts in one.
- Eustachian tube dysfunction. When the tube that ventilates the middle ear becomes blocked on one side, pressure changes muffle hearing and create a plugged sensation.
How to Tell What Type You Have
The distinction between conductive and sensorineural hearing loss is the first thing a clinician will sort out, because it narrows the list of possible causes dramatically. Conductive loss means something is blocking sound before it reaches the inner ear: wax, fluid, a damaged eardrum, a bone problem. Sensorineural loss means the nerve cells or nerve pathways themselves are affected. A basic hearing test can usually distinguish between the two in minutes.
Imaging is sometimes needed as well. A CT scan can reveal bone erosion from a cholesteatoma or a temporal bone fracture. An MRI is the standard tool for spotting an acoustic neuroma. The speed of onset, whether the loss appeared suddenly or crept in over weeks, is one of the most useful clues in determining the cause and how urgently it needs treatment.