Hearing Loss: What Could Be Causing It

The Three Types of Hearing Loss

Hearing loss falls into conductive, sensorineural, or mixed categories based on where in the auditory pathway the problem occurs. Identifying which type you have determines every subsequent diagnostic and treatment decision.

Conductive hearing loss results from anything that blocks sound transmission through the outer ear canal, tympanic membrane, or ossicular chain. Common culprits include cerumen impaction, middle ear effusion, tympanic membrane perforation, and otosclerosis. These causes are often reversible with medical or surgical intervention.

Sensorineural hearing loss (SNHL) involves the cochlea, its sensory cells, or the auditory nerve. WHO estimates that more than 1.5 billion people globally live with some degree of hearing loss, with prevalence increasing with age [1]. The distinction matters because many chronic sensorineural losses are managed with hearing technology and communication support rather than a procedure that restores the damaged sensory cells.

Mixed hearing loss combines elements of both. A patient with presbycusis who also develops chronic otitis media, for example, has a mixed pattern on audiometry. Treatment must address each component separately.

Age-Related Hearing Loss (Presbycusis)

Age-related hearing loss (presbycusis) is a common cause of hearing difficulty in later life and typically develops gradually in both ears. Difficulty understanding speech in background noise may become apparent before quiet-room deficits [22]. A markedly asymmetric or rapidly progressive pattern should not automatically be attributed to age.

In a Baltimore Longitudinal Study of Aging analysis of 681 men and 416 women screened to exclude otologic disease and noise-induced loss, hearing thresholds declined more than twice as fast in men at most ages and frequencies, although patterns varied substantially between individuals [2]. Presbycusis can reflect changes in sensory cells, the stria vascularis, neural pathways, and the cumulative effects of health and environmental exposures.

Risk factors associated with age-related hearing loss include diabetes, cardiovascular disease, smoking, and chronic noise exposure. In a population-based Beaver Dam study of 3,753 adults aged 48 to 92, current smokers were 1.69 times as likely to meet the study's hearing-loss definition as nonsmokers after adjustment [3]. That cross-sectional association does not prove that smoking cessation reverses an established loss, but it strengthens the case for addressing avoidable exposures and cardiovascular risk.

Guidance differs on proactive screening. The USPSTF found insufficient evidence to determine the balance of benefits and harms of population screening in asymptomatic adults aged 50 and older [17]. A 2024 AAO-HNSF guideline recommends screening adults 50 and older during a health care encounter, obtaining an audiogram if screening suggests loss, and considering assessment at least every 3 years for known loss or reported change [21]. Neither statement supports ignoring symptoms; perceived difficulty warrants clinical assessment.

Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) is the second leading cause of SNHL and the most preventable. It produces a characteristic 4 kHz "notch" on audiometry before spreading to adjacent frequencies.

The National Institute for Occupational Safety and Health (NIOSH) sets the recommended exposure limit at 85 dBA for an 8-hour time-weighted average, with a 3 dB exchange rate. Every 3 dB increase halves the safe exposure duration. A rock concert at 110 dB permits only 1.5 minutes of unprotected exposure before risking permanent damage 4.

NIHL occurs through two mechanisms. Acute acoustic trauma (explosions, gunshots) can rupture the tympanic membrane or dislocate ossicles, producing immediate conductive or mixed loss. Chronic exposure causes metabolic exhaustion and oxidative stress in outer hair cells, leading to gradual SNHL that patients often attribute to "normal aging."

WHO identifies unsafe personal listening and loud entertainment venues as important preventable risks for young people [5]. Once established, noise-induced sensorineural loss is generally permanent. Management centers on reducing further exposure, using effective hearing protection, monitoring when risk continues, and providing hearing rehabilitation when indicated.

Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss (SSNHL) is commonly defined in studies as a decline of at least 30 dB across three consecutive frequencies within 72 hours. The 2019 AAO-HNSF guideline estimates an annual incidence of 5 to 27 per 100,000 and emphasizes prompt recognition [6]. A person may simply notice a blocked or muffled ear, so apparent “ear congestion” should not be assumed to be wax or fluid without an examination.

The updated guideline recommends distinguishing conductive from sensorineural loss at presentation and obtaining audiometry as soon as possible, within 14 days of symptom onset [6]. Clinicians may offer corticosteroids as initial therapy within 2 weeks. For incomplete recovery, the guideline recommends offering intratympanic steroid therapy 2 to 6 weeks after onset. It also recommends evaluating for retrocochlear pathology with MRI or auditory brainstem response rather than relying on follow-up audiometry alone.

Prognosis varies with the initial severity, audiogram pattern, age, associated vertigo, and time to assessment. Most adult cases addressed by the guideline are idiopathic; clinicians should avoid presenting an unproven viral or vascular mechanism as the confirmed cause. The guideline also recommends against routine head CT, routine laboratory panels, and routine antivirals or vasoactive drugs for presumptive idiopathic SSNHL [6].

Otosclerosis and Middle Ear Causes

Otosclerosis involves abnormal bone remodeling near the oval window, which can progressively fix the stapes footplate and produce conductive hearing loss. It commonly becomes apparent in early-to-middle adulthood and may affect one or both ears.

An unselected autopsy series found histologic otosclerosis in 2.5% of 236 temporal bones. Because only a minority of histologic lesions fix the stapes, the investigators extrapolated a clinical prevalence of about 0.30% to 0.38% [7]. Histologic disease and symptomatic conductive hearing loss are therefore not interchangeable prevalence measures.

Stapedotomy or stapedectomy can improve the conductive component in appropriately selected patients, while hearing aids are a non-surgical option. Results and risks depend on anatomy, baseline cochlear reserve, the procedure, and the treating center. Sodium fluoride has been used historically, but evidence is not strong enough to present it as routine disease-modifying therapy [8].

Other conductive causes include:

• Chronic otitis media with tympanic membrane perforation or cholesteatoma
• Ossicular chain discontinuity from trauma or erosion
• Superior semicircular canal dehiscence, which produces autophony and a characteristic low-frequency air-bone gap
• Eustachian tube dysfunction with serous effusion

Ototoxic Medications

Many medicines and chemicals can affect hearing or balance. Clinically important groups include aminoglycoside antibiotics, platinum-based chemotherapy, loop diuretics, salicylates at high exposure, and some other anti-infective or antineoplastic agents. Risk depends on dose, duration, combinations, kidney function, prior hearing status, and individual susceptibility.

Cisplatin-associated hearing loss is commonly bilateral and begins at higher frequencies, but reported incidence varies widely with the population, dose, testing method, and co-exposures [9]. The FDA approved sodium thiosulfate (Pedmark) in 2022 to reduce cisplatin-associated ototoxicity in pediatric patients 1 month and older with localized, non-metastatic solid tumors; that indication should not be generalized to every cisplatin regimen [10].

Aminoglycosides (gentamicin, tobramycin, amikacin) damage vestibular and cochlear hair cells through mitochondrial oxidative stress. Gentamicin is preferentially vestibulotoxic, while amikacin is preferentially cochleotoxic. Serial audiometry during treatment allows early detection before symptomatic loss develops.

ASHA's ototoxicity guidance describes baseline and serial audiologic monitoring as a way to identify change early and support treatment decisions [18]. The test schedule should be tailored to the drug, dose schedule, baseline hearing, age, and clinical context rather than copied from a generic calendar.

Loop diuretics (furosemide, bumetanide) cause transient hearing loss by disrupting the endocochlear potential. The effect is usually reversible upon drug discontinuation but can become permanent with high-dose IV administration, particularly in patients with concurrent renal insufficiency.

Autoimmune and Inflammatory Causes

Autoimmune inner ear disease (AIED) accounts for fewer than 1% of all SNHL cases but is one of the few forms that may respond to immunosuppressive therapy. It typically presents as bilateral, fluctuating or rapidly progressive SNHL over weeks to months.

The diagnosis is clinical and specialist-led; no single biomarker confirms autoimmune inner ear disease. In a historical referral-center study, antibody to a 68-kD inner-ear protein was found in 42 of 72 patients with idiopathic progressive bilateral SNHL and correlated with active disease and steroid response [11]. Those findings do not establish a modern stand-alone diagnostic test, and improvement after a corticosteroid trial does not by itself prove an autoimmune cause.

Systemic inflammatory conditions that can include audiovestibular disease include granulomatosis with polyangiitis, Cogan syndrome, systemic lupus erythematosus, and relapsing polychondritis. The pattern, mechanism, and frequency differ by disease, so hearing loss alone does not establish one of these diagnoses.

Immunosuppressive and biologic drugs have been studied or used in selected cases, but treatment choices depend on the suspected systemic disease, severity, response, and specialist assessment. The evidence base is limited and does not support a single universal regimen.

Genetic and Congenital Hearing Loss

Genetic causes account for a substantial share of congenital and childhood hearing loss. Many genes are implicated, and GJB2-related hearing loss is a common form of autosomal recessive nonsyndromic SNHL in numerous populations [12].

Genetic hearing loss can be nonsyndromic or part of a broader syndrome. Important examples include:

• Pendred syndrome (SLC26A4 mutations): SNHL with enlarged vestibular aqueduct and thyroid goiter
• Usher syndrome: SNHL with retinitis pigmentosa, the leading cause of deaf-blindness
• Waardenburg syndrome: SNHL with pigmentary anomalies
• Branchio-oto-renal syndrome: conductive, sensorineural, or mixed loss with branchial and renal anomalies

Universal newborn hearing screening is the entry point to Early Hearing Detection and Intervention programs. The Joint Committee on Infant Hearing's 2019 position statement retains the “1-3-6” benchmark: complete screening by 1 month, confirm hearing status by 3 months, and enroll infants with hearing differences in appropriate early intervention by 6 months. Programs already meeting those targets are encouraged to work toward a “1-2-3” timeline [13].

Retrocochlear Pathology

Vestibular schwannoma (acoustic neuroma) is a classic retrocochlear cause. These benign tumors arise from Schwann cells of the vestibular portion of cranial nerve VIII. Unilateral or asymmetric hearing loss, tinnitus, and imbalance are common presenting features, although symptoms are not specific to a tumor.

Most vestibular schwannomas present with insidious unilateral hearing impairment, tinnitus, or vertigo. A systematic review found that auditory brainstem response performs better for tumors larger than 1 cm and can miss smaller lesions, while MRI strategies have substantially higher sensitivity [14]. MRI protocol and contrast use should be selected by the treating clinician and radiology team.

Management options include observation with serial MRI, microsurgical resection, and stereotactic radiosurgery. Unexplained unilateral or asymmetric sensorineural loss warrants audiologic and otolaryngology assessment; the decision to image should reflect the audiogram, associated tinnitus or neurologic findings, prior studies, and clinical judgment rather than an uncited universal threshold.

Diagnostic Approach

A systematic evaluation begins with history, otoscopy, and audiometry. The Weber and Rinne tuning fork tests provide bedside lateralization but cannot replace formal audiometry.

Pure-tone audiometry quantifies hearing thresholds at 250-8000 Hz by air and bone conduction. The air-bone gap distinguishes conductive from sensorineural loss. Speech discrimination testing (word recognition scores) differentiates cochlear from retrocochlear SNHL: scores disproportionately poor relative to pure-tone thresholds suggest neural pathology.

Tympanometry evaluates middle-ear mechanics. A flat (Type B) tracing can occur with effusion or perforation and must be interpreted with ear-canal volume and otoscopy. A shallow Type As pattern can suggest reduced mobility. Otoacoustic emissions assess cochlear outer-hair-cell function and are interpreted alongside behavioral or electrophysiologic hearing tests.

Additional studies are selected from the history, examination, and audiogram:

• MRI with gadolinium: asymmetric SNHL or suspected retrocochlear lesion
• CT temporal bones: conductive loss, cholesteatoma, superior canal dehiscence
• Targeted laboratory testing: when infection, inflammation, systemic autoimmune disease, or another specific diagnosis is suspected; routine broad laboratory panels are discouraged in idiopathic SSNHL [6]
• Genetic testing: bilateral congenital SNHL, family history, syndromic features

Treatment Options by Type

Treatment matches pathology. Conductive losses are often correctable. Sensorineural losses are managed rather than cured.

For conductive hearing loss: Cerumen removal may restore hearing when impaction is the cause. Middle-ear ventilation tubes, tympanic-membrane repair, or stapes surgery may be appropriate for selected structural problems. Air-conduction or bone-conduction hearing devices can provide rehabilitation when surgery is not suitable, is not desired, or does not fully correct the loss.

For sensorineural hearing loss: Hearing aids are a mainstay when loss affects communication. A Cochrane review of 5 randomized trials involving 825 adults found benefit for hearing-specific quality of life and listening ability in mild-to-moderate loss [15]. Cochlear implant evaluation is appropriate when appropriately fitted hearing aids provide limited speech understanding, but candidacy criteria vary by age, device labeling, insurer, and implant program; a single percentage cutoff should not be presented as universal. FDA-regulated over-the-counter hearing aids are intended for adults 18 and older with perceived mild-to-moderate hearing loss, not children or sudden, severe, or one-sided symptoms [19].

For sudden SNHL: The AAO-HNSF guideline allows corticosteroids as an initial option within 2 weeks and recommends intratympanic steroid salvage for incomplete recovery 2 to 6 weeks after onset [6]. It also allows hyperbaric oxygen only in combination with steroids, within 2 weeks as initial treatment or within 1 month as salvage. Drug, route, dose, and suitability require clinician assessment; the guideline does not support publishing one regimen as correct for every patient.

When to Seek Urgent Evaluation

Sudden hearing loss in one or both ears warrants same-day or otherwise prompt clinical assessment rather than waiting to see whether it clears. The guideline's treatment windows are measured from symptom onset: initial corticosteroids may be offered within 2 weeks, and salvage intratympanic therapy is recommended for incomplete recovery 2 to 6 weeks after onset [6]. Facial weakness, new focal neurologic symptoms, severe vertigo, head trauma, pulsatile tinnitus, or bloody/persistent drainage can signal a different urgent problem and should accelerate evaluation.

For adults with gradual bilateral loss, the USPSTF concluded in 2021 that evidence is insufficient to determine the balance of benefits and harms of screening asymptomatic adults aged 50 and older [17]. This is not a recommendation against evaluating symptoms. People reporting communication difficulty, tinnitus, asymmetry, or functional impairment should receive an appropriate hearing assessment.

Hearing loss is associated with cognitive decline in observational studies, but treatment effects need randomized evidence. In ACHIEVE, 977 adults aged 70 to 84 were randomized to a hearing intervention or health education. Cognitive change over 3 years did not differ in the combined cohort; a prespecified analysis found a different effect in the older, higher-risk ARIC subgroup [20]. That result supports further study and careful subgroup interpretation, not a promise that hearing aids prevent dementia.