Otosclerosis is a condition where abnormal bone growth inside the ear gradually locks one of the tiny bones responsible for transmitting sound, leading to progressive hearing loss. It most commonly affects adults between their 20s and 40s, and roughly 50 to 60% of people diagnosed have a family history of the condition.
How Otosclerosis Causes Hearing Loss
Your middle ear contains three of the smallest bones in your body. The last in the chain, called the stapes, sits against a membrane-covered opening to the inner ear called the oval window. When sound hits your eardrum, vibrations pass through these bones and into the fluid-filled inner ear, where they’re converted into nerve signals your brain interprets as sound.
In otosclerosis, the dense bone surrounding the inner ear starts breaking down and rebuilding itself abnormally. Bone-dissolving cells appear first, replacing healthy bone with spongy, disorganized tissue rich in blood vessels and connective tissue. Over time, this spongy tissue hardens into dense, sclerotic bone. The process typically begins right at the edge of the oval window. As the abnormal bone builds up, it either calcifies the ligament holding the stapes in place or invades the stapes footplate directly. Either way, the stapes loses its ability to vibrate freely, and sound can no longer pass efficiently into the inner ear.
In a less common but more serious form called cochlear otosclerosis, the abnormal bone growth extends around the inner ear itself, potentially damaging the sensory cells responsible for converting vibrations into nerve signals. This can cause a type of hearing loss that surgery alone cannot fix.
Who Gets It
Otosclerosis runs strongly in families. Between 50 and 60% of affected people report a relative with the same condition. Early genetic studies suggested it followed a dominant inheritance pattern with reduced penetrance, meaning you could carry the gene without developing symptoms. More recent genome-wide research paints a more complex picture: a large study analyzing over 3,500 cases identified 27 genetic risk locations, confirming that otosclerosis is polygenic, meaning many genes each contribute a small amount of risk rather than one gene acting as a clear trigger. Genes involved in bone metabolism, including one linked to collagen production, show consistent associations.
Women are diagnosed more often than men, and the condition typically appears during childbearing years. Pregnancy appears to accelerate symptoms in a meaningful number of cases. In one review of 479 women with otosclerosis, between 33 and 66% of those with bilateral disease perceived their hearing worsening during pregnancy. The hormonal connection isn’t fully understood, but the pattern is consistent enough that clinicians consider it a real factor in how quickly the disease progresses.
What It Feels Like
Hearing loss is the hallmark symptom, and it usually starts in one ear before eventually affecting both. The progression is gradual, often so slow that people don’t realize it’s happening until someone else points it out. Many people first notice they can’t hear low-pitched sounds or struggle to catch a whisper. Conversations in quiet rooms may still feel manageable while noisy environments become increasingly difficult.
Some people also experience tinnitus, a persistent ringing, buzzing, or hissing sound. Dizziness and balance problems occur less frequently but are possible, particularly if the abnormal bone growth extends toward the inner ear structures involved in balance.
How It’s Diagnosed
A hearing test is the primary tool. It measures two things: how well sound travels through your ear canal and middle ear (air conduction) and how well your inner ear responds when sound bypasses the middle ear entirely (bone conduction). In otosclerosis, air conduction is reduced because the stapes can’t vibrate, but bone conduction initially stays relatively normal. The gap between the two measurements, called the air-bone gap, is a strong indicator.
Otosclerosis also produces a characteristic dip in bone conduction scores around a specific frequency, known among audiologists as the Carhart notch. This dip, typically most prominent around 2,000 Hz, isn’t a true inner ear deficit. It’s a mechanical artifact caused by the stiffened stapes, and it often improves after successful surgery.
When imaging is needed, high-resolution CT scanning of the temporal bone can detect abnormal bone deposits as small as 1 millimeter. In the active phase, these appear as areas of reduced density near the oval window. In more advanced disease, the scan may show thickened bony plaques narrowing the oval or round windows. Cochlear otosclerosis has a distinctive appearance on CT: a halo of reduced density encircling the inner ear, sometimes called the “fourth ring.”
Surgical Treatment
The most effective treatment for otosclerosis is a procedure called a stapedectomy (or its variation, stapedotomy), where a surgeon removes part or all of the immobilized stapes bone and replaces it with a tiny prosthesis. This restores the chain of vibration from the eardrum to the inner ear.
Success rates are high. Studies consistently show that 79 to 99% of patients achieve significant closure of their air-bone gap, with most experiencing a meaningful jump in hearing ability, averaging around 26 decibels of improvement. Laser-assisted techniques tend to produce results at the higher end of that range.
Recovery is relatively quick. Most people go home the same day and return to normal routines within about a week, though full healing of the ear takes around six weeks. Air travel should be avoided during that healing window. Common short-term side effects include dizziness for the first few days and a temporary change in taste on one side of the tongue, which typically resolves within a few months. Some people develop new or worsened tinnitus. Severe vertigo or signs of infection after surgery warrant a prompt call to your surgeon.
People with physically demanding jobs may need extra time off beyond that first week. A follow-up appointment is usually scheduled about a week after surgery to check for complications.
When Surgery Isn’t the Right Fit
Not everyone with otosclerosis needs or wants surgery. If hearing loss is mild, hearing aids can effectively compensate by amplifying sound enough to overcome the mechanical blockage. For people with hearing loss in only one ear, or those who prefer to avoid surgical risk, hearing aids remain a reliable option.
Sodium fluoride has been used as a medical treatment with the goal of slowing disease progression by stabilizing bone remodeling. Only one double-blind, placebo-controlled trial has been conducted, and it found a reduced rate of hearing deterioration after two years in the treatment group. Several other studies have reported similar trends, but the overall evidence remains low quality, and there’s no consensus on ideal dosing or how long treatment should continue. It’s sometimes considered for cochlear otosclerosis, where the abnormal bone threatens the inner ear and surgery alone can’t address the damage.
Conductive vs. Sensorineural Hearing Loss
Most otosclerosis causes conductive hearing loss, meaning the problem is mechanical: sound can’t physically reach the inner ear properly. This is the type surgery fixes well. But when abnormal bone encroaches on the inner ear itself, it can cause sensorineural hearing loss, where the nerve pathways are affected. Many people with advanced otosclerosis end up with a mix of both, called mixed hearing loss. The conductive component responds to surgery or hearing aids, while the sensorineural component is permanent. In cases of profound sensorineural loss from cochlear otosclerosis, cochlear implants may be considered.