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Variables Regarding Noise-Induced Hearing Loss

One of the most frequently seen hearing losses is caused by noise exposure. Noise that is damaging to the delicate system of hearing can be heard from chainsaws, guns, skill saws, heavy equipment, carpentry power tools, landscaping equipment, motorcycles and off-road vehicles. A good rule of thumb is if you need to raise your voice to be heard over a noise, that noise could potentially cause hearing loss. Other factors to consider is the length of time you are exposed to loud sound and the actual loudness of the noise. Gunfire is so loud that length of time does not apply. Only one gunshot can cause permanent damage to hearing of the person shooting and/or the person standing near the gunshot.

Length of Time Exposed to a Sound

The Occupational Safety and Health Administration (OSHA) is the government agency that implements guidelines for safe working conditions in the workplace. OSHA enforces safety in the workplace. The current standard for allowable workplace noise is eight hours of exposure to 90dBA and two hours of exposure to 100dBA sound. Properly fitted hearing protection is recommended for anyone exposed to sound 85dBA or more. The National Institute for Occupational Safety and Health (NIOSH) is responsible for conducting research and making recommendations for the prevention of work-related injury and illnesses. NIOSH has made more conservative recommendations compared to the OSHA recommended exposure limit. NIOSH recommends eight hours of exposure to 85dBA, one hour at 94dBA.

These sound exposure limits are recommended while a person wears properly fitted hearing protection! You may wonder why should I limit the time I am exposed to noise if I am wearing hearing protection. The answer may surprise you. The best fitting hearing protectors might give you 25dB to 31dB of reduction in sound; however, this figure is true if an audiology professional places the hearing protection on an individual and then tests the amount of sound reduction produced. The average individual will not place the hearing protection in or over his or her ears with the same amount of skill, which means you will not get even that much protection.

Why the limited amount of protection? Because sound bypasses your ears and goes through your skull, stimulating or vibrating the hearing organs causing hearing loss. The take-away message is: Hearing protection does not prevent hearing loss under certain conditions.

Lifestyle, Genetics Play a Role in Hearing Loss

We have known for years that smoking puts people at risk for developing hearing loss. The smoke may affect the hearing of the person smoking, the hearing of persons exposed to secondhand smoke and a baby in utero. Teens exposed to smoke are two to three times more likely to develop hearing loss compared to those with little or no smoke exposure. How does smoking affect hearing? The nicotine and carbon monoxide lower oxygen blood levels and constrict blood vessels all over the body, including the vessels responsible for maintaining the inner ear. The smoke interferes with the neurotransmitters in the auditory nerve responsible for telling you what sounds you are hearing. Smoking may cause inflammation of the eustachian tube and lining of the middle ear. This type of inflammation puts the smoker at a much higher risk for ear infections. Secondhand smoke is a known cause of chronic middle ear infections. Children who live with a smoker have a 37 percent higher risk of developing middle ear infections and a 62 percent higher risk if the smoker is their mother.

Genetic research is showing a correlation between an individual’s genetics and their susceptibility to suffer hearing loss after noise exposure. One study identified 34 genes whose variants are associated with human noise-induced hearing loss. The roles measured for the various genes in this study were oxidative stress response, cell communications, DNA repair, apoptosis (death of individual cells as a function of growth) and gene regulation. A person’s genetics creates different susceptibility to noise-induced hearing loss. This would account for the varying degree of hearing loss, the amount of tinnitus and damage that causes difficulty recognizing sounds or words. Animal studies are underway to gain a better understanding of the relationship of the genetic structure of an animal and the amount of hearing loss sustained after noise exposure. It is a complicated but exciting area of study, which may one day help determine the best way to protect hearing despite excessive noise exposure. FBN

By Karon Lynn, Au.D.

Trinity Hearing Center is located at 1330 N. Rim Dr., Suite B in Flagstaff. For more information, visit TrinityHearing.net.


Karon Lynn is a doctor of audiology with 30 years of experience working with hearing impaired individuals. Dr. Lynn may be reached at 928-522-0500 or at audio@trinityhearing.net.


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