Noise - Its Effects on Hearing and Tinnitus

Home > Hearing Issues > About Noise > Noise - Its Effects on Hearing...

What Is Noise?
Noise is by definition, unwanted sound. It varies in its composition in terms of frequency, intensity and duration. Sounds that are pleasing to some people may be unpleasant to others. For example, loud rock music is enjoyable to some, but others find it offensive. Thus, for a sound to be categorized as a noise, it must be judged as such by the listener.

Protect Your Ears From Noise!
Many of the sounds in our environment that we classify as noise are annoying but not loud enough to cause damage to our hearing. Other sounds, however, are of such high intensity that they are dangerous to the ear and may cause permanent hearing loss and/or tinnitus. Noise is everywhere and we cannot always escape being exposed to it. When noise exposure can’t be avoided, protective measures can be taken to limit or possibly prevent ear damage.

Noise-Induced Hearing Loss
Continuous exposure to high levels of noise can cause hearing impairment in some individuals. There is considerable variation from person to person regarding susceptibility to noise. However, standards have been established that indicate how much sound an average person can tolerate without experiencing damage to their hearing. Although this level remains somewhat controversial, it has been established that most people will not experience a hearing loss if the noise levels do not exceed 85 to 90dBA. Therefore, the Occupational Health and Safety Act (OSHA) established criteria based upon an 8-hour duration of exposure to a 90dBA level of continuous noise. It was felt that these criteria would protect approximately 90% of the people exposed to 90dBA levels for a significant part of their lifetime. For shorter duration's of exposure, higher noise levels that are known to specifically induce tinnitus.

Table 1
Permissible Noise Exposures

Duration per Day (hours)	Noise level (dBA)
8	90
6	92
4	95
3	97
2	100
1.5	102
1	105
0.75	107
0.5	110
0.25 or less	115

Danger! Noise Can Hurt You
Many sounds in our environment exceed the OSHA standards and continuous exposure to these sounds could cause loss of hearing. The difference in decibel levels is greater than might be expected: one hundred times more sound energy enters the ear in a 95dB environment than in a 75dB environment.

The typical hearing loss observed with patients who have a long history of on-the-job noise exposure is characterized by a loss of hearing in the frequency range between 3000 and 6000 Hz. In the early stages of exposure, a temporary loss will be observed at the end of a working period but will disappear after several hours. Continuous exposure to the noise will result in a permanent hearing loss that will be progressive in nature and become subjectively noticeable to the employee over time. These changes in hearing thresholds can be monitored through audiometric testing and will alert clinicians that preventive measures should be initiated. In its advanced stages, a loss of hearing in the high frequencies will seriously affect the person’s ability to understand normal speech. In general, patients with hearing losses limited to the high frequencies will not experience difficulty detecting speech, but will have trouble understanding it.

Noise-Induced Tinnitus
Tinnitus, a ringing or other noise in the ears or head, is most often a subjective experience. It can be intermittent or constant; mildly annoying or, for some, very distressing. Although the exact cause of tinnitus is unknown, many patients who have a history of noise exposure have tinnitus. Noise is by far the most probable cause of tinnitus, and it may or may not occur simultaneously with hearing loss. Most patients who have tinnitus also have hearing problems, but a small percentage (fewer than 10%) have hearing within normal limits. Many patients have hearing losses without tinnitus.

(It is reasonable to assume that any symptom associated with ear pathologies – hearing loss, tinnitus, sound sensitivity, dizziness, pain, or a feeling of fullness in the ear – could occur individually or without other symptoms.)

Tinnitus, as a result of noise exposure, can occur suddenly or very gradually. When it occurs suddenly, it is often perceived at a fairly loud volume and may persist at that level permanently. However, for some, the tinnitus is temporary and does not return.

More commonly, the onset of noise-induced tinnitus is gradual and intermittent in its early stages. Patients report hearing a mild form of tinnitus for a short period of time following a lengthy exposure to loud sounds. Once the patient is removed from the noise source, the tinnitus soon disappears and is inaudible until the next exposure. This intermittent pattern often continues for months or years with the periods of tinnitus becoming longer and longer.

Eventually the tinnitus is constant. If exposure to the offending noise continues, the tinnitus often increases in volume.