Noise-Induced Hearing Loss Definition
Noise-induced hearing loss (NIHL) is a hearing disorder that occurs due to exposure to high-intensity sounds, generally over a prolonged time period. It is a preventable condition that is known to affect people of all demographics and age groups.
What Happens in Noise-Induced Hearing Loss?
Every day we listen to sounds in our environment, like the sounds that emanate from the radio or the television, household appliances as well as the traffic. These sounds reach our ears at safe levels and do not detrimentally affect our hearing. On the other hand, when our ears get exposed to harmful noises, i.e., sounds that are either too loud or last for a long time or both, the sensitive structures which are present within the inner ear can get damaged, thereby giving rise to noise-induced hearing loss. These sensitive structures, known as hair cells, are tiny sensory cells that help in converting sound energy to electrical signals that are then transmitted to the brain. However, once these hair cells are damaged, they cannot grow back which eventually leads to permanent deafness.
Noise-Induced Hearing Loss Epidemiology
People of all ages and all ethnic backgrounds have been known to be affected by this disorder. Around 15% of Americans between 20 and 69 years of age have been affected by NIHL; the figures closing around 26 million.
Noise-Induced Hearing Loss Effects
A long-time exposure to harmful sounds can damage the auditory nerve and the hair cells. Impulse sounds can cause immediate hearing loss which may become permanent. It can be accompanied by signs of tinnitus – a buzzing, ringing or roaring sensation felt in the ears. Although it may gradually subside over time, patients may experience spells of tinnitus occasionally or constantly throughout their lifetime. One or both of the ears might get affected by it.
Continuous exposure to high-pitched, loud noises can damage the structures of the hair cells, thereby leading to Tinnitus and hearing loss, although it occurs in a slower pace than that of impulse noises.
Sometimes, an exposure of impulse and/or continuous noise can lead to a temporary hearing loss. It is referred to a temporary threshold shift if the affected individual regains hearing after a period of time that can last for anywhere within 16-48 hours.
Noise-Induced Hearing Loss Types
NIHL can be divided into 2 types, based on the intensity of the loud noise as well as the length of time of exposure. These two basic types are stated and discussed below:
NIHL resulting from acoustic trauma
NIHL caused by an acoustic trauma occurs when permanent cochlear damage takes place from a single exposure to an excessively loud sound pressure. This type of NIHL generally results from an exposure to sounds having a very high intensity, such as gunfire, explosions, firecrackers and loud hitting of a large drum.
Gradually developing NIHL
This type of NIHL occurs when permanent cochlear damage is caused by repeated exposure to various loud sounds occurring over a long period of time. This form is not caused by a single encounter with a high intensity sound pressure, a feature that is the hallmark of NIHL caused by acoustic trauma. Gradually developing noise-induced hearing loss can occur due to multiple exposures to various sounds with excessive volume, such as stereo systems in homes and vehicles, nightclubs, concerts, personal media players and excessive noises in the workplace. According to the U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA), an exposure to noises of 85 dB (A) or more for more than 8 hours per day might lead to permanent hearing loss. This scale is known as exposure action value. As the decibel scale is based on logarithms, an increase in the sound pressure by 3 decibels doubles the intensity of sound, which can quicken the speed of hearing loss.
Noise-Induced Hearing Loss Causes
NIHL can result from a single exposure to some form of intense “impulse” sound or by a continuous exposure to high-pitched noises that last over a long period of time, like a noise generating from a woodworking shop. The higher the decibels of the sound, the greater are the chances of developing hearing loss. The duration of the sound as well as closeness to the source of sound are also deciding factors that determine the effects of sound on an individual.
There are also a number of occupations in which the working people are greatly susceptible to hearing loss. These include the following:
- Orchestra conductors
Noise-Induced Hearing Loss Symptoms
The signs and symptoms of NIHL increase gradually when an individual is exposed to high-pitched noises over a prolonged period of time. Over time, the various sounds an individual hears can slowly get distorted and/or muffled. The affected individual can also experience difficulty in understanding speech. Someone with this condition might not be aware of this hearing loss, even though it can be observed by conducting a hearing test.
One of the reasons why people often are unable to notice the dangers of loud noises is that only very few symptoms are caused by prolonged exposure. Hearing loss hardly even causes any pain. The symptoms that are commonly felt include vague sensations of fullness or pressure in the ears, verbal speech sounding muffled or seeming to be coming from a long distance, and tinnitus or a ringing sensation in the ears. These signs may take minutes, hours or even days to go away after the initial exposure to the noise ends.
People often assume that their ears have returned to their normal state once the symptoms go away. However, this is hardly true. Even if no presence of symptoms can be felt, some of the inner ear cells may have suffered damage from the noise. If enough number of healthy cells is present in the inner ear, the hearing may return to normal. Nevertheless, a long-lasting hearing loss will develop if the exposure to the loud noise is repeated, thereby leading to cellular destruction.
The first signs of NIHL involve an inability to hear high-pitched noises, like singing of the birds, or being unable to understand speech while standing in a large crowd or where there is much background noise. With prolonged damage, hearing further declines and it becomes more and more difficult to detect lower pitched sounds.
The various signs and symptoms of NIHL are listed below:
- Loss of sensitivity
- Tinnitus or head noise
- Temporary threshold shift
- High frequency hearing loss
- Ear discomfort after exposure
- Difficulty hearing in background noise
Noise-Induced Hearing Loss Diagnosis
Various audiometric tests are conducted to see if an individual is having NIHL. These include:
- Noise surveys
- Personal dosimetry
- Screening audiometry
- Pure-tone audiometry
- Speech reception threshold (SRT) test
- Cortical evoked response audiometry (CERA)
Noise-Induced Hearing Loss Differential Diagnosis
A number of conditions exhibit signs and symptoms similar to that of NIHL. Hence, while determining the diagnosis of NIHL, it should be differentiated from such similar conditions in order to come up with the best treatment plan. The differential diagnoses of NIHL include conditions such as:
- Ototoxicity of the inner ear
- Presbycusis of the inner ear
- Otosclerosis of the middle ear
- Sudden hearing loss of the inner ear
- Autoimmune disease of the inner ear
- Genetic sensorineural hearing loss of the inner ear
Noise-Induced Hearing Loss Treatment
There are a number of management options for individuals having NIHL that can improve hearing abilities and facilitate communication. These include usage of hearing aids such as earplugs and/or earmuffs, FM systems and counseling. Some research suggests that it is possible to manage the symptoms of hearing loss by administering high doses of magnesium for a short period of time. This treatment should be started as quickly as possible after the exposure to loud noise. Sticking to a magnesium-rich diet prior to any exposure to loud sound is also helpful in preventing NIHL. However, this mode of treatment should be handled carefully as consuming high quantities of magnesium can be detrimental to one’s health.
A number of health conditions can exacerbate the symptoms of NIHL. Due to this reason, effective management of these disorders is required to positively influence the progression of NIHL treatment. These include:
- Diabetes mellitus
- Cardiovascular disease
- Exposure to various ototoxic drugs
There are no medical options at present for patients of NIHL who had been exposed to loud noise for more than a week ago. However, research is being conducted to discover genetic and drug therapies that can help to eradicate the symptoms of NIHL.
Noise-Induced Hearing Loss Prognosis
The prognosis for NIHL patients is excellent with proper sound amplification and counseling. Recent advancements in the field of digital hearing aid technology, like open-fit hearing aids, directional microphones, as well as more advanced algorithms have enhanced the positive outcome of NIHL treatment. The initial treatment should be followed by annual audiological evaluations to see if there are any changes in the patient’s hearing as well as to modify the hearing-aid prescriptions.
Noise-Induced Hearing Loss Prevention
Although there are no treatment methods that can permanently reverse the damage of the hair cells, following certain preventative measures can negate further chances of damage and protect the ears. These include the following:
- Reducing exposure to loud noises
- Developing the habit of using earplugs or earmuffs prior to being exposed to loud noises for long periods of time
- Using sound-absorbing materials that reduce noise at the workplace and at home
- Avoiding the use of several noisy machines simultaneously
- Avoiding the tendency to drown out various unwanted noises by increasing other sounds, such as the sounds of headsets, television or car radios
- Going to the doctor annually for the evaluation of hearing abilities of sufferers
Written by Prasenjit Banerjee
on May 19th, 2013. The article was last updated on May 19th, 2013