Hearing loss has three categories defined by where the problem is. Sensorineural hearing loss is damage in the inner ear or auditory nerve — usually permanent, most often caused by aging (presbycusis), noise exposure, genetic factors, ototoxic medications, sudden idiopathic loss, or viral and metabolic conditions. Conductive hearing loss is in the outer or middle ear — often treatable — caused by earwax impaction, middle-ear fluid or infection, eardrum perforation, otosclerosis, or foreign objects. Mixed hearing loss is both at once. The simplest way to tell which you have is an audiogram with both air-conduction and bone-conduction thresholds; a gap between them indicates a conductive component. Sensorineural loss is what hearing aids are designed for; conductive loss often needs medical treatment first.
The three types of hearing loss
Audiologists classify hearing loss by anatomy: where in the auditory pathway the problem is. The classification matters because it determines what kind of treatment is appropriate — medical, surgical, or amplification.
1. Sensorineural hearing loss (inner ear or nerve)
The cochlea is a snail-shaped inner-ear organ lined with thousands of microscopic hair cells. Each hair cell is tuned to a specific frequency. When sound reaches the cochlea, the hair cells move, generating electrical signals carried by the auditory nerve to the brain. Damage to either the hair cells or the nerve is sensorineural hearing loss.
Hair cells do not regenerate in humans, which is why sensorineural loss is usually permanent. It is also the most common type of hearing loss in adults. Hearing aids are designed primarily for this category.
2. Conductive hearing loss (outer or middle ear)
Sound must travel from the outside world through the ear canal, vibrate the eardrum, and then transmit through three tiny middle-ear bones (the ossicles) into the cochlea. Anything that blocks or dampens that path produces conductive hearing loss. Many conductive causes are medically or surgically treatable.
3. Mixed hearing loss
Mixed loss has both a conductive component and a sensorineural component. An older adult with age-related sensorineural loss and impacted earwax has mixed loss. So does someone with a chronic middle-ear condition plus noise damage. Each component is addressed separately.
Sensorineural causes
Age-related hearing loss (presbycusis)
The most common cause of hearing loss in adults. Hair cells in the cochlea are damaged or lost progressively with age, typically starting in the high frequencies and moving lower. The NIDCD reports that roughly one in three U.S. adults aged 65–74 has hearing loss, rising to nearly half of those 75 and older. The pattern on an audiogram is a sloping curve, worse at higher frequencies.
Noise-induced hearing loss
Chronic exposure to loud noise — occupational, recreational, or both — damages cochlear hair cells. The damage accumulates over years and produces a characteristic notch on the audiogram, classically around 4 kHz. The NIDCD notes that exposures above roughly 85 dBA over an 8-hour day produce measurable risk. See our full article on noise-induced hearing loss for prevention and recovery details.
Sudden sensorineural hearing loss
Hearing loss that develops over 72 hours or less, typically in one ear, often idiopathic (no identified cause). The 2019 AAO-HNS Clinical Practice Guideline (Chandrasekhar et al.) classifies this as a medical priority and recommends audiometric confirmation within 14 days of onset and corticosteroid treatment within 2 weeks of symptom onset. See our sudden hearing loss article.
Ototoxic medications
Several drug classes can damage cochlear hair cells:
- Aminoglycoside antibiotics (gentamicin, tobramycin, streptomycin, amikacin).
- Platinum-based chemotherapy (cisplatin, carboplatin).
- Loop diuretics at high doses (furosemide, ethacrynic acid).
- Some antimalarials (quinine, chloroquine derivatives at sustained doses).
- High-dose aspirin and other salicylates — usually temporary.
If you have started a new medication and noticed hearing change, ask your prescriber.
Genetic and congenital causes
Several hundred genes have been associated with hearing loss; some cause syndromic hearing loss (along with other features), some are non-syndromic. Genetic causes can present at any age, including adult-onset patterns.
Head injury
Concussion, skull fracture, or significant acoustic trauma (a single very loud event, such as an explosion) can damage the cochlea or auditory nerve.
Viral and bacterial infections
Mumps, measles, meningitis, and a few other infections can damage the inner ear. Cytomegalovirus is a leading congenital cause of sensorineural hearing loss in newborns; in adults, post-viral sudden hearing loss is occasionally seen.
Ménière's disease
A chronic inner-ear condition characterised by episodic vertigo, fluctuating hearing loss, tinnitus, and a sense of ear fullness. Typically affects one ear initially and is diagnosed clinically.
Acoustic neuroma (vestibular schwannoma)
A benign tumour on the vestibulocochlear nerve. Often presents with asymmetric hearing loss, one-sided tinnitus, or balance changes. Rare, but a reason any persistent one-sided hearing loss warrants MRI.
Autoimmune inner-ear disease
Rare; presents with bilateral, progressive sensorineural loss over weeks to months and may respond to immunosuppressive therapy.
Conductive causes
Earwax (cerumen) impaction
The most common reversible cause of hearing loss. The 2017 AAO-HNS Clinical Practice Guideline on Earwax (Cerumen Impaction) defines the condition and outlines safe management. Removal by a clinician using irrigation, suction, or curette typically restores the affected hearing within minutes. See our article on what's reversible.
Otitis media (middle-ear infection or effusion)
Fluid or pus in the middle ear behind the eardrum dampens sound transmission. Common in children; less common but possible in adults. May resolve on its own or require medical treatment.
Eustachian tube dysfunction
The eustachian tube equalises pressure between the middle ear and the throat. When it doesn't open properly — during a cold, after flying, with allergies — pressure imbalance produces fullness and conductive loss.
Eardrum perforation
A hole in the eardrum from infection, sudden pressure change, or trauma. Many small perforations heal on their own; larger ones may need surgical repair (tympanoplasty).
Otosclerosis
Abnormal bone growth around the stapes (the smallest middle-ear bone), reducing its ability to vibrate. Usually presents in adulthood with progressive conductive or mixed loss. Surgical treatment (stapedectomy) is highly effective; hearing aids are an alternative.
Cholesteatoma
An abnormal skin growth in the middle ear, often a complication of chronic ear infection. Damages middle-ear bones over time. Requires surgical removal.
Foreign objects
More common in children but possible in adults — cotton tip fragments, hearing aid domes, or other small objects retained in the canal can cause sudden conductive loss.
How clinicians determine the cause
A typical evaluation has three parts:
- History. Onset (sudden or gradual?), pattern (one ear or both?), associated symptoms (pain, drainage, tinnitus, dizziness, neurological symptoms), exposure history (noise, ototoxic drugs, head injury), family history.
- Examination. Visual examination of the ear canal and eardrum (otoscopy) to identify earwax, fluid, perforation, foreign objects.
- Audiometry. A full audiogram with both air-conduction and bone-conduction thresholds. A gap between air and bone thresholds (an "air-bone gap") indicates a conductive component. Overlapping air and bone thresholds at abnormal levels indicate sensorineural loss. Both gap and abnormal bone thresholds indicate mixed loss.
For asymmetric sensorineural loss or other red flags, MRI of the internal auditory canals may be added.
What the cause means for treatment
- Sensorineural loss — usually permanent. Hearing aids are the primary intervention. Cochlear implants are an option for severe-to-profound loss with limited benefit from hearing aids. See OTC vs prescription hearing aids.
- Conductive loss — often treatable. Earwax removal, infection treatment, surgical repair of perforations or otosclerosis can restore hearing. Hearing aids can supplement when medical treatment is not possible.
- Mixed loss — treat the conductive part first, then address the residual sensorineural component with hearing aids.
The bottom line
The cause of hearing loss is anatomical: inner ear (sensorineural), outer/middle ear (conductive), or both (mixed). The most common adult cause is age-related sensorineural loss, followed by noise-induced sensorineural loss; the most common reversible cause is earwax impaction. An audiogram with both air and bone conduction is the single most useful test for distinguishing categories, and the category determines whether the right next step is medical, surgical, or amplification.
References
- National Institute on Deafness and Other Communication Disorders (NIDCD), NIH. Age-Related Hearing Loss (Presbycusis). nidcd.nih.gov/health/age-related-hearing-loss
- NIDCD, NIH. Noise-Induced Hearing Loss. nidcd.nih.gov/health/noise-induced-hearing-loss
- NIDCD, NIH. Sudden Deafness. nidcd.nih.gov/health/sudden-deafness
- Schwartz SR, Magit AE, Rosenfeld RM, et al. Clinical Practice Guideline (Update): Earwax (Cerumen Impaction). Otolaryngology – Head and Neck Surgery. 2017;156(1 Suppl):S1–S29. doi:10.1177/0194599816671491
- Chandrasekhar SS, Tsai Do BS, Schwartz SR, et al. Clinical Practice Guideline: Sudden Hearing Loss (Update). Otolaryngology – Head and Neck Surgery. 2019;161(1 Suppl):S1–S45. doi:10.1177/0194599819859885
- World Health Organization. World Report on Hearing. Geneva: WHO; 2021. who.int/publications/i/item/9789240020481