Conduction deafness, more commonly called conductive hearing loss, happens when sound waves are physically blocked from reaching the inner ear. Any obstruction or damage in the ear canal, eardrum, or the three tiny bones of the middle ear can cause it. Earwax buildup, middle ear infections, fluid behind the eardrum, abnormal bone growth, and a ruptured eardrum are all possible causes.
How Sound Normally Travels Through the Ear
Sound vibrations enter the ear canal, hit the eardrum, and pass through a chain of three small bones (the malleus, incus, and stapes) suspended in the middle ear. These bones amplify the vibrations and deliver them to the fluid-filled inner ear, where nerve cells convert them into electrical signals for the brain. Conductive hearing loss means something is interrupting that mechanical chain before vibrations ever reach the inner ear.
On a hearing test, conductive loss shows up as an “air-bone gap,” meaning sounds played through the air are heard much worse than sounds transmitted directly through the skull bone. That gap can range from 0 to 60 decibels depending on the severity of the blockage.
Earwax and Foreign Objects
The simplest cause is a physical blockage in the ear canal. Compacted earwax can muffle sound significantly, and it’s one of the most common reasons for a sudden, reversible drop in hearing. Small objects lodged in the canal, particularly in children, produce the same effect. Once the blockage is removed, hearing typically returns to normal immediately.
Middle Ear Infections and Fluid
Middle ear infections (otitis media) are one of the most frequent causes of conductive hearing loss, especially in children. When the space behind the eardrum fills with fluid, the eardrum and bone chain can’t vibrate freely. Even after an active infection clears, fluid can linger for weeks or months, a condition called otitis media with effusion.
The hearing loss from trapped fluid is usually mild to moderate, but it can reach 30 to 40 decibels, roughly the difference between hearing a normal conversation clearly and hearing it as a muffled whisper. The thickness of the fluid matters: thin, watery fluid causes less hearing loss than thick, mucus-like fluid. In children, this level of hearing reduction during key developmental years can affect speech and language learning if it persists.
Chronic or repeated infections can also cause lasting structural damage to the eardrum or the bones behind it, turning a temporary problem into a permanent one.
Otosclerosis: Abnormal Bone Growth
Otosclerosis is a condition where abnormal bone deposits form around the stapes, the last and smallest bone in the middle ear chain. The stapes normally vibrates freely to pass sound into the inner ear, but as new bone locks it in place, it gradually stops moving. The result is a slow, progressive hearing loss that usually affects both ears and tends to appear in early adulthood.
Because the inner ear itself is healthy, otosclerosis is one of the most surgically treatable forms of hearing loss. A procedure called stapedectomy replaces the fixed stapes bone with a tiny prosthetic. Studies of over 500 patients show that about 62% achieve near-complete closure of the air-bone gap (within 10 decibels of normal), and success rates across the literature range from 54% to 86%.
Ruptured Eardrum
A hole or tear in the eardrum prevents it from vibrating properly, reducing the energy transferred to the middle ear bones. Common causes include sudden pressure changes (diving, flying, or a slap to the ear), loud explosions, and poking the ear canal with objects like cotton swabs. Infections that build up pressure behind the eardrum can also cause it to rupture. Most small perforations heal on their own within a few weeks, but larger tears may require surgical repair.
Ossicular Chain Disruption
The three middle ear bones are delicate and connected like links in a chain. If any link breaks or separates, the chain can no longer transmit vibrations effectively. The most common cause of this disruption is head trauma, particularly from car accidents, falls, and physical assaults. A blow to the head can dislocate these bones even without fracturing the surrounding skull bone.
Blast injuries and sudden pressure changes (barotrauma) can also separate the bones. Cholesteatoma, an abnormal skin growth in the middle ear, may slowly erode the bones over time. If six weeks after a head injury someone still has conductive hearing loss with an intact eardrum, ossicular chain dislocation is the presumed cause.
Eustachian Tube Dysfunction
The eustachian tube connects the middle ear to the back of the throat and equalizes air pressure on both sides of the eardrum. When this tube stays swollen or blocked, often from allergies, colds, or sinus infections, negative pressure builds up in the middle ear. This pulls the eardrum inward and can draw fluid into the space, both of which dampen sound transmission. You’ve likely felt a mild version of this during a cold or on an airplane when your ears feel “full” and sounds seem muffled.
Congenital Ear Abnormalities
Some people are born with structural differences that cause conductive hearing loss from birth. Microtia is a condition where the outer ear is underdeveloped, and atresia is the absence or closure of the ear canal. Without a functioning canal to funnel sound to the eardrum, sound transmission is severely reduced. These conditions can affect one or both ears.
For people with atresia or other malformations that can’t be corrected with conventional hearing aids, bone-anchored hearing devices offer an alternative. These implants bypass the outer and middle ear entirely, transmitting sound vibrations through the skull bone directly to the inner ear. They’re particularly effective for bilateral cases and for patients who haven’t responded well to reconstructive surgery.
Growths and Tumors
Cysts, benign tumors, and cholesteatomas (abnormal skin growths) in the ear canal or middle ear can physically block sound or erode the structures that transmit it. Cholesteatomas are particularly problematic because they expand slowly, destroying bone as they grow. Left untreated, they can erode the ossicular chain and cause permanent hearing loss. These growths typically require surgical removal.
How Conductive Loss Is Identified
Two classic bedside tests use a tuning fork to distinguish conductive hearing loss from nerve-related (sensorineural) hearing loss. In the Rinne test, a vibrating tuning fork is placed on the bone behind the ear, then held next to the ear canal. Normally, sound through air is louder than through bone. If bone conduction sounds louder, that’s a “negative” Rinne result and points to conductive loss, meaning vibrations reaching the inner ear through the skull are getting through fine, but the air pathway is blocked.
The Weber test places the tuning fork on the center of the forehead. In conductive hearing loss, the sound lateralizes to the affected ear, because background noise isn’t masking the bone-conducted sound on that side. These two tests together give a quick initial picture, though formal audiometry is needed to measure the exact degree and pattern of loss.
The key distinction with conductive hearing loss is that the inner ear and auditory nerve are working normally. The problem is purely mechanical, which is why many causes are treatable or even fully reversible once the obstruction or damage is addressed.