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Noise-induced hearing loss (NIHL) is one of the most common hearing problems encountered in adults. Depending on the reference, it has been estimated that there are somewhere between 10 and 22 million Americans with NIHL. Although the most common source of damaging noises is found in the workplace, the increasingly clamorous sounds of everyday life encountered in the home and during leisure-time activities make NIHL a predicament that affects all members of society, regardless of age, gender, or ethnic group. The Centers for Disease Control and Prevention, for example, recently reported from one of their surveys that over 5 million American youths exhibit some degree of hearing loss due to exposure to noise at hazardous levels.
My interest in noise exposure and hearing-loss prevention began many years ago as a graduate student. Research that I conducted as part of my dissertation requirement showed how exquisitely sensitive individual cells of the inner ear were to moderately loud sounds, even when the comparable population response showed few exposure-induced deficits. Later on as a junior-faculty researcher, I was able to reproduce these results in comparable studies conducted in human volunteers. That is, certain biological measures of the aftereffects of over-exposure to moderately intense levels of sound showed that they produced a long-lasting dysfunction that was unexpected based on an accompanying normal tone-detection capability. In other words, the finer biological assay inferred sounds were more damaging than their counterpart measures of behavioral hearing indicated.
Scientists determined many years ago that excessive noise of sufficient intensity and duration could damage the ear and result in permanent hearing loss due to irreversible damage to the inner ear’s sensory hair cells. It is known too that typical NIHL occurs slowly and over time as a cumulative process. Thus, chronic exposure to loud sounds accumulates in time to gradually produce irreversible damage to the sensory cells (hair cells) of the inner ear. From recent research, it is also known that NIHL damages the delicate hair cells by triggering the formation of molecules called free radicals that cause hair cell death.
One relevant area of research with respect to the powerful new audio technology that needs attention is the resiliency of a child’s auditory system following noise exposure. Although it is well-accepted in the scientific literature that the auditory system is more fragile in very young experimental models, this has clearly, for ethical reasons, never been deliberately established in young humans. We know for certain, however, that earbuds permit sounds to be louder in smaller ear canals and to deliver potentially dangerous noises closer to the sensitive inner ear structures. Also, the longer battery life of personal stereo systems allows for long-duration exposures. And, loud sounds delivered over long periods of time clearly lead to the insidious destruction of cochlear components. It is such exposures that eventually and unavoidably lead to an elevation in hearing levels, along with other common symptoms of hearing impairment including tinnitus, muffled hearing, and difficulties in understanding ordinary speech in the presence of background noise. Given the potentially long life ahead of young children and teens, in particular, developing hearing loss because of exposure to hazardous sounds early on promises to lead to a life-time of hearing problems.
Because NIHL is preventable, the consumer needs to be educated about the dangers of being exposed to high levels of noise over long periods of time. The educational role of the hearing-health professional is paramount for the conservation of hearing that is threatened by habitual noise exposure. For certain, the American Speech-Language-Hearing Association is among the professional societies that is taking an important role in educating consumers about the dangers of excessive sound exposure.
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