Lower levels of noise may cause permanent hearing damage

Research suggests that levels of noise that are currently thought to result in
only a temporary loss of hearing, may in fact cause permanent hearing damage.
As the authors Sharon G. Kujawa and M. Charles Liberman explain in The Journal
of Neuroscience, "temporary" noise-induced hearing loss can lead to Cochlear
Nerve Degeneration.

Overexposure to intense sound can cause temporary or permanent hearing loss.
Post-exposure recovery of threshold sensitivity has been assumed to indicate
reversal of damage to delicate mechano-sensory and neural structures of the
inner ear and no persistent or delayed consequences for auditory function.

The authors show, using cochlear functional assays and confocal imaging of the
inner ear in mouse, that acoustic overexposures causing moderate, but
completely reversible, threshold elevation leave cochlear sensory cells intact,
but cause acute loss of afferent nerve terminals and delayed degeneration of
the cochlear nerve.

Results suggest that noise-induced damage to the ear has progressive
consequences that are considerably more widespread than are revealed by
conventional threshold testing. This primary neurodegeneration should add to
difficulties hearing in noisy environments, and could contribute to tinnitus,
hyperacusis, and other perceptual anomalies commonly associated with inner ear

More info - Source: The Journal of Neuroscience