Hearing loss caused by prolonged exposure to excessive noise or by brief exposure to intensely loud noise. Exposure to a sudden, very loud noise, usually above 130 decibels, can cause immediate and permanent damage to hearing. Normally, muscles in the middle ear respond to loud noise by altering the position of the ossicles (the chain of bones that pass vibrations to the inner ear), thus damping down the intensity of the noise. If these protective reflexes have no time to respond, the full force of the vibrations is carried to the inner ear, severely damaging the delicate hair cells in the cochlea. Occasionally, loud noises can rupture the eardrum. More commonly, noise damage occurs over a period of time by prolonged exposure to lower levels of noise. Any noise above 85–90 decibels may cause damage, with gradual destruction of the hair cells of the cochlea, leading to permanent hearing loss. Prolonged exposure to loud noise leads initially to a loss of the ability to hear certain high tones. Later, deafness extends to all high frequencies, and the perception of speech is impaired. Eventually, lower tones are also affected. Sounds at 85–90 decibels or above may cause pain and temporary deafness. Prolonged tinnitus (ringing or buzzing in the ears) occurring after a noise has ceased is an indication that some damage has probably occurred.
Noise-induced hearing loss |
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