Industry workers often have NIHL because the discomfort threshold is not a relevant indicator of the harmfulness of a sound. Gradually developing
Gradually developing NIHL refers to permanent cochlear damage from repeated exposure to loud sounds over a period of time. Unlike acoustic trauma, this form of NIHL does not occur from a single exposure to a high-intensity sound pressure level. Gradually developing NIHL can be caused by multiple exposures to excessive noise in the workplace or any source of repetitive, frequent exposures to sounds of excessive volume, such as home and vehicle stereos, concerts, nightclubs, and personal media players. Earplugs have been recommended for those people who regularly attend live music concerts. A range of earplugs are now available ranging from inexpensive disposable sets to custom fit, attenuated earplugs which provide true fidelity at reduced audio levels. Personal listening devices
Although research is limited, it suggests that increased exposure to loud noise through personal listening devices is a risk factor for noise induced hearing loss. More than half of people are exposed to sound through music exposure on personal devices greater than recommended levels. Research suggests stronger correlations between extended duration or elevated usage of personal listening devices and hearing loss. Workplace
About 22 million workers are exposed to hazardous noise, with additional millions exposed to solvents and metals that could put them at increased risk for hearing loss. Occupational hearing loss is one of the most common occupational diseases. 49% of male miners have hearing loss by the age of 50.
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Damaged sensory hairs (stereocilia) of the hair cells; damaged hair cells degenerate and die. In humans and other mammals, dead hair-cells are never replaced; the resulting hearing loss is permanent. Inflammation of the exposed areas. This inflammation causes poor blood flow in the exposed blood vessels (vascular stasis), and poor oxygen supply for the liquid inside the cochlea (endolymphatic hypoxia) Those noxious conditions worsen the damaged hair cell degeneration. Synaptic damages, by excitotoxicity. Noise overstimulation causes an excessive release of glutamate, causing the postsynaptic bouton to swell and burst. However the neuron connection can be repaired, and the hearing loss only caused by the "wiring" (i.e. excitotoxicity) can thus be recovered within 2–3 days. Hair cell damage or death
When the ear is exposed to excessive sound levels or loud sounds over time, the overstimulation of the hair cells leads to heavy production of reactive oxygen species, leading to oxidative cell death. In animal experiments, antioxidant vitamins have been found to reduce hearing loss even when administered the day after noise exposure. They were not able to fully prevent it. Antioxidants however do not seem to be effective in protecting the human ear. Damage ranges from exhaustion of the hair (hearing) cells in the ear to loss of those cells. NIHL is, therefore, the consequence of overstimulation of the hair cells and supporting structures.