11Hyperacusis, Misophonia and Sound Tolerance

FThree faces of decreased sound tolerance

Some patients are not troubled by an internal sound so much as by external sounds the rest of us ignore. This umbrella is called decreased sound tolerance, and it has three distinguishable faces [2015]. Hyperacusis is an abnormal intolerance of ordinary-level sound based on its physical loudness — everyday noises feel uncomfortably or even painfully loud. Misophonia is a strong emotional and physiological reaction to specific trigger sounds (often human sounds such as chewing or breathing), driven by the meaning of the sound rather than its volume. Phonophobia is fear or anticipatory anxiety about sound, an avoidance-driven variant.

The categories overlap and frequently coexist in the same patient, but separating them matters because they respond to different management.

TDefining hyperacusis precisely

A working definition frames hyperacusis as unusual tolerance to ordinary environmental sounds — reduced loudness-discomfort levels — that is not explained by simple recruitment alone [2014]. Subtypes are described: a loudness form (sounds are too loud), an annoyance form, a fear form (overlapping phonophobia), and a pain form in which moderate sound provokes genuine aural pain. Loudness-discomfort-level testing helps quantify it.

It is not rare. Among patients attending a tinnitus and hyperacusis clinic, a meaningful proportion have hyperacusis severe enough to drive avoidance and functional impairment, and it commonly travels with tinnitus, anxiety and insomnia [2018]. Crucially, hyperacusis is distinct from recruitment, which is the abnormally rapid growth of loudness above a raised threshold seen in cochlear hearing loss.

TMisophonia as a defined disorder

For years misophonia lacked an agreed definition. A 2022 Delphi consensus settled it: misophonia is a disorder of decreased tolerance to specific sounds or their associated stimuli, in which exposure to trigger sounds provokes intense emotional (anger, disgust, anxiety) and physiological reactions that the person recognises as disproportionate, leading to distress and functional impairment, and not better explained by another condition [2022]. Triggers are typically repetitive human-generated sounds, and a strong attentional and associative learning component is recognised in the neurophysiological model [2015].

The defining feature is that the reaction is keyed to the identity and meaning of the sound, not its loudness — a turned-down television still triggers if it carries the offending sound. This separates misophonia cleanly from hyperacusis.

CA shared central-gain mechanism

Hyperacusis and tinnitus share a unifying thread: increased central auditory gain [2013]. When peripheral input is reduced or perceived as inadequate, central auditory neurons up-regulate their responsiveness. This homeostatic compensation can manifest as a phantom sound (tinnitus) and as exaggerated responsiveness to real sound (hyperacusis), which is why the two so often coexist. Limbic and autonomic networks then attach emotional valence, accounting for the distress and the misophonic and phonophobic overlays.

Because the mechanism is one of over-responsiveness, the instinctive patient strategy of avoiding sound and over-using earplugs is counterproductive: sound deprivation can further raise central gain and worsen tolerance over time.

CWhy it changes tinnitus management

Identifying decreased sound tolerance reshapes the management plan. Aggressive masking or loud sound therapy aimed at the tinnitus can be intolerable to a hyperacusic patient and must be introduced gently, often with sound desensitisation at low, comfortable levels rather than masking. Recommending blanket ear protection is usually wrong — structured, graded sound enrichment is preferred. Misophonia needs a different lever again: management leans on counselling, attention and reaction-focused therapy, and trigger management rather than on loudness manipulation. Mislabelling all three as “just sensitive ears” leads to the wrong treatment and an unhappy patient.