The leading cause of adult-onset hearing loss is the effects of aging on the auditory system. Almost half the people in the United States older than age 65 have some degree of hearing loss.
Hearing loss is defined as one of three types:
Hearing loss in the older population is caused not only by the degenerative effects of aging on the cochlea but also by the accumulated effects of exposure to noise and ototoxic drugs. Approximately 104 million people in the United States are exposed to levels of noise that can cause hearing loss, and 1 in 4 adults in the United States has measurable hearing loss caused by exposure to harmful noise. Even among people who report that their hearing is “excellent” or “good,” nearly 20% have audiometric evidence of noise-induced hearing loss.
Various chemicals and drugs adversely affect the auditory system; the main ones in clinical use are amino-glycoside antibiotics and cisplatin, both of which are toxic to sensory hair cells. Hearing loss develops in approximately 20% of patients receiving amino-glycosides.
The prevalence of sudden, idiopathic hearing loss is 5 to 20 cases per 100,000 population, with approximately 4000 new cases per year in the United States. Sudden sensorineural hearing loss, is defined as the onset of hearing loss over a period of 72 hours or less in one or both ears.
An epidemiological study has shown that the age-adjusted prevalence of hearing loss is declining in the United States, however. Explanations for this include a possible decrease in a reduction in exposure to occupational noise as a result of fewer manufacturing jobs and more widespread use of hearing protection, cessation of smoking, and better management of cardiovascular risk factors. Although the prevalence of hearing loss increases with age, it is not inevitable. More awareness should be brought to potentially damaging and slowly cumulative effects of exposure to loud sounds such as the common sources. Hearing protection includes using ear protectors (earmuffs or earplugs), avoiding or limiting time spent in loud venues, using personal music systems at moderate volumes, and wearing noise-canceling headphones or earphones.