Hearing Loss Types: Sensorineural, Conductive and Mixed Hearing Loss

Audiologists commonly describe hearing loss as sensorineural, conductive or mixed. Understanding the difference makes audiograms, ENT letters and military hearing records far easier to read — and it stops an abnormal test being labelled "military deafness" before anyone has looked at the ear itself.

The short version

How hearing normally works

Sound enters the outer ear, reaches the eardrum and middle ear, and the middle-ear bones transmit that vibration into the cochlea in the inner ear. The cochlea converts vibration into nerve activity travelling towards the brain. A problem at different points along that pathway produces different types of hearing loss.

NICE puts the basic division simply: hearing loss may be caused by interference with the transmission of sound from the outer to the inner ear — conductive — or by damage within the cochlea, the auditory nerve or auditory centres in the brain — sensorineural.

Conductive hearing loss

Conductive hearing loss means sound is reduced or blocked before it properly reaches a functioning inner ear. The problem lies in the outer ear, ear canal, eardrum, middle ear or middle-ear bones. Causes include earwax, middle-ear fluid, ear infection, a perforated eardrum, damage to the middle-ear bones, otosclerosis and other structural problems.

Whether it is permanent depends entirely on the cause. Earwax can be removed. Many middle-ear infections and fluid resolve or can be treated. Other problems may need surgery or longer-term rehabilitation — NHS guidance notes, for instance, that otosclerosis may be improved with hearing aids or surgery. That is very different from established NIHL, where damaged inner-ear structures do not regenerate.

People often describe conductive loss as "muffled" or "blocked", sometimes with pressure, pain, discharge or fullness. But symptoms alone cannot classify a hearing loss — a sensorineural loss can sound muffled too. Testing is what separates them.

Sensorineural hearing loss — and why it is not a synonym for NIHL

Sensorineural hearing loss means the problem lies principally in the inner ear or auditory nerve pathway. It is usually permanent, and it is the broad category into which ordinary noise-induced hearing loss falls.

But the causes are many: ageing, excessive noise, some ototoxic medicines, infections, genetic causes, certain medical conditions, and head or ear injury. NICE is explicit that in adults the most common cause of sensorineural hearing loss is presbycusis — age-related loss.

Audiogram shape gives clues but is not a fingerprint. Noise injury can produce characteristic high-frequency features; age-related loss commonly affects high frequencies too; other disorders produce other patterns. Abbott uses contrasting illustrative audiograms to show how stereotypical NIHL and age-associated loss differ, while repeatedly insisting on diagnosis from the full clinical and exposure picture rather than shape alone.

Mixed hearing loss

Mixed hearing loss means a sensorineural component and a conductive component exist in the same ear. As UCLH puts it, there is a problem in the outer or middle ear at the same time as damage to the inner ear or the nerve pathway to the brain, and the symptoms and causes may be a mixture of both.

Someone might already have permanent sensorineural NIHL and later develop earwax or middle-ear disease. Their current test would then contain both components. Having one hearing problem does not protect anyone from developing another — which is why a new deterioration should not automatically be filed as "my military hearing loss getting worse".

Blast is the military route to this. The British Society of Audiology notes that a conductive element attenuates sound and to that extent protects the inner ear — but adds that acoustic trauma can itself cause conductive losses via tympanic membrane perforation and disruption of the ossicular chain. A severe blast could therefore produce inner-ear injury, middle-ear injury, or both, and the resulting loss may be sensorineural, conductive or mixed. Our acute acoustic trauma guide covers the immediate clinical side.

How the types are told apart: air and bone conduction

Air conduction uses headphones or insert earphones and tests the whole normal pathway — outer ear, middle ear, inner ear. Because sound has travelled the entire route, poor air-conduction thresholds can result from either a conductive or a sensorineural problem. Air conduction alone often cannot separate them.

Bone conduction uses a small vibrating transducer against the skull. Abbott's judicial primer describes it precisely:

An air–bone gap means the air-conduction threshold is poorer than the corresponding bone-conduction threshold: the inner ear responds better than the normal outer-and-middle-ear route suggests. That indicates a conductive component — but not which one. It does not distinguish wax from fluid from eardrum damage from another middle-ear problem.

Why masking matters, and why bone thresholds stop at 2 kHz

Bone-conduction vibration stimulates both cochleae, so the audiologist may not know which ear actually responded. Abbott states the consequence bluntly:

Masking introduces controlled noise into the non-test ear so it cannot answer for the ear being assessed. The same problem arises in air-conduction testing where hearing differs substantially between ears: sound presented to the poorer ear can cross the skull and be detected by the better one, producing a falsely good threshold. Masking is a technical necessity, not decoration on the chart.

What a military surveillance audiogram can and cannot tell you

This is where the distinction earns its place for veterans. Abbott separates diagnostic pure-tone audiometry from occupational surveillance audiometry, and records that the surveillance procedure it identifies — BSA Recommended Procedure Surveillance Audiometry 2023 — does not involve bone-conduction testing. It also notes that the BSA pure-tone audiometry procedure of 2018 does not cover screening or automated audiometry. Those are two different documents doing two different jobs.

So a surveillance audiogram can be valuable evidence about hearing thresholds at a point in time. It may show deterioration, asymmetry, a high-frequency pattern, or change from an earlier baseline. But if it contains only air-conduction thresholds, it may not independently establish whether an elevated threshold represented sensorineural, conductive or mixed loss.

A current diagnostic assessment is different because it can combine air conduction, bone conduction, masking where indicated, ear examination, clinical history and further tests. Abbott says an audiogram can quantify both the degree and type of hearing loss and calls audiometry critical for diagnostic purposes. Our guides to reading a military audiogram and military medical records cover the symbols and the record types in detail.

The practical question when you look at any hearing record is simply: are both air and bone thresholds present? If not, be cautious about assigning a type of hearing loss from that chart alone.

Other tests can help too. Tympanometry assesses how the eardrum and middle-ear system respond to pressure changes, and can be useful where conductive loss is suspected. It does not replace pure-tone audiometry, and it does not diagnose military NIHL.

Asymmetry, sudden loss and when to act

Unilateral or markedly asymmetric hearing loss can need further investigation. NICE says unexplained unilateral or asymmetric loss may warrant specialist referral, and recommends considering MRI in sensorineural hearing loss where there is an asymmetry of at least 15 dB at two adjacent specified frequencies. That is a clinical investigation rule — not a formula for deciding whether asymmetry came from weapons.

Military NIHL genuinely can be asymmetric: weapon orientation, head position and exposure circumstances differ between the ears. But significant asymmetry has other causes too, so it should be investigated rather than automatically explained away as firearms exposure.

The conductive/sensorineural distinction matters enormously here, because a blocked ear from wax and a sudden sensorineural hearing loss can both feel like "my ear suddenly went muffled". Nobody can reliably tell those apart from sensation alone. That is exactly why assessment exists.

What this means for a claim

A military hearing-loss claim concerns what military noise caused. Suppose a current audiogram shows 50 dB of hearing loss. That figure alone does not tell anyone how much is sensorineural, whether a conductive component exists, how much is age-associated, how much is noise-induced, or when each part developed. The medico-legal task is far more specific than showing that hearing is worse than normal.

A mixed audiogram does not defeat a military-noise history — the sensorineural part may well include military NIHL, and the conductive component then needs separating and understanding. What it does mean is that the total current loss should not be attributed wholesale to military noise. Equally, an acute conductive problem at the time of testing can temporarily overstate the underlying sensorineural impairment, which is why the ear's condition on the day matters to interpretation.

Two shortcuts to avoid. Hearing-aid benefit does not identify the type — that is a rehabilitation question, not a diagnostic one. And tinnitus does not identify the type either: it commonly accompanies sensorineural noise damage, but it coexists with other ear disorders too.

The most useful records tend to be a combination: recruitment audiograms, later military surveillance audiograms, diagnostic audiograms containing bone conduction, ENT records, NHS audiology records, and anything describing ear disease or injury. The practical skill is recognising what kind of test each record actually contains — a row of air-conduction thresholds is not automatically a complete diagnostic assessment.

Common questions