Why Do Some People Become Deaf?
In the course of our daily interactions we will often come into contact with one or more people who appear to experience some degree of hearing impairment. By contrast, we are far less likely to encounter an individual who is totally deaf. In practice, this is a condition that is seen to exhibit varying degrees of severity and, in professional circles; the latter term is one that is reserved to describe an individual in whom the loss of hearing is complete while it is now general practice to refer to partial hearing loss as impairment. But why is it that some people will succumb to this condition while others remain unaffected?
Firstly, one may totally dismiss the natural process of slow auditory degradation that is the simple and quite normal result of aging. The condition begins in middle age and has no basis in pathology and it will not normally manifest to any significant degree until very late in life. By contrast, however, it is likely that most people have or will experience some degree of unnatural hearing loss, even if it is just a temporary condition. It takes little more than exposure to loud noises to give rise to the temporary state and this will often be experienced even by young when people attending pop concerts or discotheques. However, continued exposure to such as that commonly experienced by workers in a manufacturing plant may gradually result in more permanent damage unless suitable ear protectors are both provided and worn conscientiously.
When estimating the likelihood of impairment in such circumstances as well as the possibility that those exposed may even, in time, become deaf, the level of risk is normally assessed by measuring both the decibel value of the offending noise and the number of hours of exposure. The combination required to cause harm can, however, vary quite significantly between individuals. For those that may live close to a major highway or a busy airport, the risk can be especially high despite the stringent noise abatement measures imposed upon airlines in most countries. Worldwide, about 5% of the population suffer noise-induced hearing loss (NIHL).
Genetics may also give rise to an entire cocktail of conditions leading to mild and even profound losses and may be causes by both dominant and recessive genes. These conditions are relatively rare but when present may sometimes effect entire families across successive generations.
Illnesses are a more common precursor of the condition, with measles, mumps and meningitis high on the list of offenders. Adenoids that fail to atrophy can eventually obstruct the Eustachian tubes and lead to conductive hearing loss, an instance in which a simple surgical procedure can sometimes reverse the impairment completely. Even the unborn infant is not exempt from the effects of infection and sexually-transmitted diseases such as Chlamydia and Syphilis may result in children that will eventually lose their hearing. Though no infective agent is involved alcoholism in mothers is another disease that exposes infants to a similar risk.
Perversely, in treating infections, certain antibiotics such as gentamycin have also been implicated as causative agents while the list of so-called ototoxic substances that includes anti-inflammatories, anti-malarials and diuretics, keeps growing and, with pesticides, heavy metals and carbon monoxide, threatens to leave even more people deaf.