• One of the first sign of noise-induced hearing loss that individuals notice is difficulty understanding speech, especially in noisy settings. Another is a ringing in the ears in very quiet settings.

• Noise-induced hearing loss can be caused by very loud, but short burst of sound (e.g. gunshots, fireworks) or quieter, but sustained sounds (e.g. power tools and other heavy machinery).

• Thirty-two percent of Americans do not know that the regular use of household appliances, such as vacuum cleaners and lawn mowers, can cause noise-induced hearing loss. (NIOSH)

• Forty-eight percent of adults believe they have incurred some hearing loss, but only 39 percent of them have had a hearing test in the past 3 years. (Harris)

• Noise-induced hearing loss is the most common work-related condition. Approximately 30 million Americans are exposed to hazardous noise levels at work.

• Of the 73 percent of Americans who go to see fireworks, 54 percent say that they do not plan on wearing hearing protection (Harris poll).

• When used simultaneously, household appliances that do not cause harmful sound levels individually, can reach sound levels that are harmful.

• Noise-induced hearing loss always occurs at specific frequencies, which happen to be associated with speech recognition, independent of the frequency of the harmful sounds.

Interview #1:

They Don't Hear What They're Missing

William H. Slattery III, M.D., is in private practice at the House Ear Clinic in Los Angeles. He is also director of the clinical research department at the House Ear Institute and is professor of otolaryngology at the University of Southern California. The House Ear Institute, where Dr. Slattery directs the Clinical Studies Department, is one of the foremost research centers in the world.

Q-How does noise cause damage to the ear and hearing?

A- Exposure to excessive sound levels can traumatize the inner ear and cause hearing loss. As an example, when you are exposed to a loud and noisy environment, such as a rock concert, you may experience what is called a temporary threshold shift. Your hearing is noticeably diminished but seems to fully return after a period of time. It's believed that one of two things happens in this situation. Either the excessive noise caused the hair cells in the inner ear, known as the cochlea, to temporarily swell and not function or, the noise caused some of the hair cells to actually die and possibly regenerate. We are not sure which of these two mechanisms actually occur in humans.

So, what typically happens with damage to the ear is that there is an initial swelling of the hair cells. Potentially, with repeated trauma, there can be death of the hair cells. In some animal species, regeneration of the hair cells has been observed. This happens because within the inner ear, the hair cells sit on top of supporting cells on the basilar membrane of the inner ear. We know that in some specie the supporting cells can actually transform and become new hair cells. (Smolders, Ding-Pfennigdorff)

We don't know if regeneration occurs in humans, because we can't sacrifice people's inner ears in order to look in them and tell whether this is occurring. In bird species we know that hair cell regeneration occurs. There are some studies of mammal species that are currently being conducted to determine how hair cell regeneration occurs in the inner ear.

Q-What can people do about noise-induced hearing loss?

A-The most important thing with noise-induced hearing loss is prevention. We know that works. Unfortunately, in the past, noise-induced hearing loss and even hearing loss in general has not been thought of as a significant problem. So people tend to listen to loud music or they work in a loud environment without regard for the potential harm to their hearing.

Q-Has there been an increased risk of noise-induced hearing loss due to the conventions of modern society?

A-In some respects, the risk of noise-induced hearing loss has decreased as we have gone from a farming/industrial-based society to an information society. Today, risk of excessive noise levels is more likely to occur from recreational activities, as opposed to industrial noise levels. So, yes, there has been a shift. If you think back to the old farm communities, everyone had a big tractor that they used for six to eight hours a day and cars were awfully noisy in comparison to today's standards. So while there is quite a bit of noise in our society, the effect of the cumulative noise has to reach a certain level before we become concerned about its impact on hearing. Even though there is more noise in our environment -- computer noise, traffic noise -- most of it is at such a low level that it's not harmful to the ears.

The cumulative effects that cause noise-induced hearing loss are contingent on the loudness of the noise and extended exposure. You can also get noise-induced hearing loss from a single exposure to a short burst of loud noise. (National Institute on Deafness and Other Communication Disorders (NIDCD), Fact Sheet on Noise-Induced Hearing Loss, NIH Pub. No. 97-4233, April 1999) I don't want to create the misperception that noise-induced hearing loss is only cumulative and therefore people can go to the occasional loud concert or shoot guns from time to time without using hearing protection.

The cumulative effects that cause noise-induced hearing loss are contingent on the loudness of the noise and extended exposure. You can also get noise-induced hearing loss from a single exposure to a short burst of loud noise. (National Institute on Deafness and Other Communication Disorders (NIDCD), Fact Sheet on Noise-Induced Hearing Loss, NIH Pub. No. 97-4233, April 1999) I don't want to create the misperception that noise-induced hearing loss is only cumulative and therefore people can go to the occasional loud concert or shoot guns from time to time without using hearing protection.

Q-Even if you are not exposed to damaging noise levels on a daily basis, say only two hours a week, can there be a lifetime cumulative effect that leads to hearing loss?

A-Noise levels over 85 to 90 dB, for more than eight hours can be damaging to the ear. One thing that is not really clear is that there are some individuals who are much more sensitive to noise than others. The military is now becoming more interested in noise-induced hearing loss, for obvious reasons. There is a study out of Israel, where recruits were given magnesium supplements and other recruits were given no magnesium supplements. The investigators found that those who had received the supplements experienced less hearing loss from noise exposure, thus a protective effect was demonstrated. (Attias, et al, Am J Oto 15(1)1994 pp 26-32) Now that's one study, but it indicates, in my mind, that there are some susceptibility factors that may make some individuals more likely to experience noise-induced hearing loss than others.

Q-How long does it take to notice or detect noise-induced hearing loss?

A-It depends whether you are talking about noticing it or detecting it. Noticing implies that the person perceives they have a problem, whereas detecting means we can test for the hearing loss. Often with noise-induced hearing loss the first indication that we see is the person complains of ringing in the ears or tinnitus. Other symptoms that may also occur include trouble hearing in noisy situations, or difficulty hearing conversations.

It's the old frog in boiling water analogy. They say that if you put a frog in water and slowly turn up the temperature, all of sudden the water is boiling and you kill the frog. The frog never jumps out of the water because you gradually increased the temperature. If hearing loss is gradual, people are often not aware of the change in their hearing. So the hearing slowly gets worse over time and people say "No, I don't have any hearing loss," but when they take a hearing test it will show they do. They don't hear what they're missing.

Q-When people do come in for hearing tests because of ringing in their ears, how bad is the hearing loss at that point?

A-It can be anything from a very mild loss, in the range of 10 decibels, to significant loss. I have some people come in for a hearing evaluation and after looking at their results, I have to ask them "How are you functioning in life with such poor hearing." But again, because the hearing loss occurred gradually, they're not aware of what's happened.

Q-What treatments are available for noise-induced hearing loss?

A-Prevention is the most important aspect of noise induced hearing loss. Prevention may occur by avoiding excessive noise, wearing hearing protection such as earplugs, earmuffs, or in-the-ear monitors. Modification of lifestyle or the use of supplements such as magnesium may be helpful for prevention of noise induced hearing loss.

Once the hearing loss has been identified and fully evaluated, corrective measures can be considered. There are many options for hearing improvement through assistive technology such as hearing aids, and other listening devices.

Q-What do you see as the future direction of research in this field?

A-Scientists at our institute are exploring inner ear development, the maturation of the inner ear, and hair cell regeneration in order to understand how damage and repair occur in the inner ear. This should lead to new developments and treatments of inner ear hearing loss.

There are no current clinical trials in humans for noise-induced hearing loss. However, just as magnesium supplements have shown some beneficial effect at preventing noise-induced hearing loss, antioxidants are currently being investigated for the same purpose. There's a group in San Diego that is looking at some antioxidants for their protective benefit. When given to animals before prolonged noise exposure, say 48 hours antioxidants protect their ears from significant damage. (Kopke)

The future for treatment of noise-induced hearing loss becomes more promising as we understand more about the cellular mechanisms of the inner ear. Our understanding of these mechanisms will lead to prospective drug treatment of noise-induced hearing loss.

Interview #2:

Hearing Loss is 100 Percent Preventable

Peter Rabinowitz, M.D., Ph.D. assistant professor and director of clinical services in the Occupational and Environmental Medicine program at Yale University's School of Medicine. His clinical work with the program has involved diagnosing and counseling patients who have suffered noise-induced hearing loss. His current research project is looking into the susceptibilities and risk factors for noise-induced hearing loss.

Q-What kind of noises pose the greatest risk of hearing loss??

A- We know that more noise is worse, but I don't think it's really understood well yet what is a safe level. There is some growing consensus that noises as low as 82 decibels on a regular basis, eight hours a day for a long period of time for example, will cause hearing loss in some people. (Prince, M et al.?) OSHA has set the limit at 90 decibels, so they don't get very excited about 82 decibels. But I certainly feel that, if chronically exposed, even at 82 decibels some people will lose their hearing at a faster rate than others their age.

Q-How long does it take to notice hearing loss??

A-In general, if you are overexposed transiently -- let's say you go to a concert without any hearing protection -- you will immediately afterwards notice some symptoms, such as ringing in your ears. For awhile it may also feel like you have cotton in your ears and things just seem muffled.

That sort of temporary change you can notice right away. The onset of the permanent change is a more insidious and gradual thing. There is a lot of variability in terms of when people start noticing that. People also tend to notice it more in some situations than others. One of the first things people with the onset of gradual noise-induced hearing loss may notice is the ringing in their ears if they're in a very quiet place. So, in a real quiet room they may notice the ringing more when they're trying to sleep or something like that. Later in the course of hearing loss, they'll notice problems with speech discrimination, especially when there is any kind of background noise. People tend to notice it more when they're in a noisy restaurant or trying to talk with people when there is background noise, such as in a crowded room. Some people may notice it then even if they don't notice it at any other time.

The other thing that makes it hard to appreciate the loss is that the low frequency speech sounds are not affected at first. So people will be able to hear all the vowels, which are somewhat lower in frequency than the consonants, at the same intensity for a long time after developing noise-induced hearing loss. (Smoorenberg, GF-Speech Reception…?) So it seems to them like they hear just as well but they can't understand what someone is saying. They say "I hear you but I can't understand you." They don't think of themselves as deaf, because it's just as loud as it always was, but people are mumbling more than they used to. It's a subtle thing in that way.

Q-How long does it take for the hearing loss to be measurable?

A-There is some evidence that with high frequency loss of as little as 15 to 20 decibels, which is still within the range of normal variability, you start getting some trouble with speech discrimination in a noisy setting. (Smoorenberg) If you're really attuned, even a fairly minor loss will produce problems with speech discrimination.

Q-Based on occupational experience, what type of noise-induced hearing loss should people expect?

A-For most people who are exposed to environmental levels of noise, on the street and in restaurants, it's intermittent enough and it's low level enough that usually the psychological effects are greater than the effects on hair cells.

My bias, coming from the occupational setting, is that the noise just tends to be louder and more of it in a workplace. What I worry about on the environmental side is the recreational music, like night clubs. I have been pretty impressed with the noise level in night clubs. I was also impressed with lawn equipment and power tools that people would be around for a long period of time without any kind of ear protection. But of all the environments I was really impressed most with the night club scene. There is definitely the potential for hearing loss if you go to enough clubs.

Q-What about listening to music on headphones?

A-There is some evidence that you can get up to 105 decibels on those headsets. If you work out the math, listening to a headset at 105 decibels for an hour a day, you are definitely able to cause long-term damage. (Meyer-Bisch, CM Epidemiology Evaluation-Audiology?)

Q-Do you agree there has been a shift from industrial noise exposure to environmental exposure?

A-In industry now, OSHA regulates noise above 85 decibels and as a result of that regulation, a lot of noises have come down to the level of around 90 decibels in that setting. But you can see from the environmental noise survey, some sounds were louder than 90 decibels. You have to remember that every time you go up 3 decibels, you have doubled the amount of noise. But the question is how intermittent is that noise, how long-lasting is it. If it's just a siren on the street, at 95 decibels for only a few seconds, that's not too bad. If you go to a night club and it's 102 decibels and you're there for three hours, that's a lot of exposure if you go regularly. And if you listen to headphones and they're 102-105 decibels and you listen regularly that's really bad too. So, environmental exposures do have the potential to get louder than even common occupational exposures. Then the question becomes how frequently are you exposed to them.

Q-What kind of counseling is effective for encouraging prevention? A-In general, doctors are not very used to counseling and it's not something talked about by a wide range of people. If you counsel someone about noise, you're often the first person to counsel them about it. It's not like cholesterol where people have heard it a hundred times. Another difficulty is that we live in a society where noise is often equated with positive values like power. For example, a person buys a motorcycle and takes the muffler off to make it sound more powerful. And music. My daughter likes to turn it up as loud as possible, because it sounds better when it's really loud. You're up against a cultural thing where noise and power, noise and excitement are linked in many ways. And to tell people that noise is potentially dangerous sounds like you're being a wet blanket; it sounds like one more puritanical message about health.

One thing that can be effective is doing a hearing test and showing someone that they have evidence of noise-induced hearing loss. That really brings it home to that person. It can also be helpful to hear from people who have significant noise-induced hearing loss. My understanding is that Pete Townshend from The Who has pretty significant hearing loss and has been out counseling people about the dangers of noise exposure.

Q-What options are there for correcting hearing loss?

A-There may be some misperception that when your hearing goes you can just fix it with a hearing aid, the way you can fix your vision with reading glasses. People don't realize that hearing aids do not really correct the problem totally and you can never get hearing back after you've lost it.

Even though hearing aids are getting better and better, they still only amplify the sound and can't correct for the fine discrimination between different types of sound. So you get louder sounds, but there still may be some distortion and speech discrimination will still be impaired even with a hearing aid. Hearing aids only allow you to make use of the few hair cells left even though they are often damaged as well.

Q-Beyond wearing ear protection and avoiding noise, is there anything else people can do to reduce the risk of noise-induced hearing loss?

A-We need to find ways to cut down on sources of noise. That can involve things like getting manufacturers of home tools to make them quieter, which we don't really push for, to get them to label how noisy the machinery is, which again we don't really do. But just remember that this kind of hearing loss is 100 percent preventable and there's not that many things that are that easily prevented.

Q-Do you generally recommend a type of hearing protection?

A-There are a lot of different types, but, for example, cotton does not work very well as hearing protection. The most important thing in using hearing protection is to wear it correctly. Most of the ear plugs or other protective devices that are commercially available are all capable of working if you use them correctly.

CASE STUDY: Decibels Defined

The unit used to express the intensity of sound or sound pressure, the decibel was named after Alexander Graham Bell. It is measured on a logarithmic scale in which 0 dB approximates the threshold of hearing in the mid frequencies for young adults and in which the threshold of discomfort is between 85 and 95 decibels and the threshold for pain is between 120 and 140 decibels.

Although sound levels under 85 decibels are generally considered safe, some people may have hearing damage with prolonged exposure to noise levels of as little as 82 decibels. For example, sound levels from common lawn equipment, such as gas mowers, leaf blowers and chain saws range from 90 to 115 decibels. Other power tools, such as belt sanders and drills, can create noises volumes of 95 to 100 decibels. Football stadiums are filled with noises 90 to 110 decibels loud and city traffic can reach 100 decibels, according to the National Campaign for Hearing Health. (www.hearinghealth.net)

These sound levels can producing hearing loss in a matter of hours with unprotected exposure. A combination of them increases the sound level to even more damaging levels.

Even safe sound levels can become potentially damaging when they occur simultaneously. Sound levels from household appliances such as vacuum cleaners, coffee grinders and garbage disposals, rise 3 to 5 decibels, placing them in the dangerous range.

Even more dangerous, fireworks produce bursts of noise as loud as 130 to 190 decibels, which can cause hearing loss in a matter of seconds. Handgun and rifle fire reaches 160 to 170 decibels which, if close to the ear, can cause hearing loss almost instantaneously.

Recent Findings Suggest Urban Setting Means More Noise Exposure and More Hearing Loss:

-Americans are exposed to damaging noise levels on a routine basis, which helps explain why more than 5 million children in the United States have some noise-induced hearing loss.

One of the worst sound offenders in a national survey of noise levels in urban settings was night clubs, which reached sustained levels of well over 100 decibels. Restaurants also clocked in within a range of 80 to 96 decibels and street traffic levels reached 90 decibels and more when passing sirens were taken into account. (Noise Center)

That survey, which was coordinated by the Noise Center at the League of the Hard of Hearing, also suggests that people are exposed to potentially damaging levels of noise in such common settings as fitness classes, construction sites, movie theaters and video arcades.

Director of the Noise Center, Nancy Nadler, explains that they were inspired to conducted the survey when they noticed that more people were coming into their hearing clinic at a younger age.

Some hearing loss may also be due to hobbies or even household chores, according to a Wisconsin study. Noise exposure from wood and metal working, riding loud motorcycles and yard work using power tools was associated with a 10 to 20 percent increased risk of hearing loss. Wood working alone increased the risk by more than 30 percent. (Dalton 2001)

Another recent study analyzed national survey data collected by the government as part of The Third National Health and Nutrition Examination Survey. That study revealed that 12.5 percent of children ages 6 to 19 years old, have incurred permanent damage to their ears' hair cells. The researchers estimate that this amounts to 5.2 million American children with hearing loss caused by exposure to loud noises. (Niskar 2001)

That study also showed that 15.5 percent of children ages 12 to 19 years old had some hearing loss in one or both years, highlighting the fact that noise-induced hearing loss only grows more prevalent with age.

The Research:

1. NIDCD Fact Sheet on Noise-Induced Hearing Loss. 1999 Washington, DC:Health and Human Services, NIH Pub. No. 97-4233.

2. Noise and Hearing Loss. NIH Consens Statement Online 1990 Jan 22-24 [2001 May 3]; 8(1):1-24.

3. Rabinowitz, P.M. (2000). Noise-induced hearing loss. Am Fam Physician 61, 2749-2756, 2759-2760.

4. National Institute for Occupational Safety and Health (NIOSH). Noise Induced Hearing Loss: Attitudes and Behaviors of U.S. Adults. Washington, DC: Health and Human Services, 1998.

5. Harris Interactive poll conducted for the National Campaign for Hearing Health. (June 2000) [Americans risk noise-induced hearing loss on fourth of July].

6. National Institute for Occupational Safety and Health (NIOSH). Fact Sheet: Work-Related Hearing Loss. Washington, DC: Health and Human Services, 1999.

7. National Campaign for Hearing Health. Toxic noise: Background information. www.hearinghealth.net

8. Smoorenburg, G.F., de Laat, J.A., Plomp, R. (1982). The effect of noise-induced hearing loss on the intelligibility of speech in noise. Scandinavian Audiology. Supplementum 16, 123-133.

9. Ding-Pfennigdorff, D., Smolders, J.W., Muller, M., Klinke, R. (1998). Hair cell loss and regeneration after severe acoustic overstimulation in the adult pigeon. Hearing Research, 120(1-2), 109-120.

10. Attias J., Weisz, G., Almog, S., Shahar, A., Wiener, M., Joachims, Z., Netzer, A., Ising, H., Rebentisch, E., Guenther, T. (1994). Oral magnesiumintake reduces permanent hearing loss by noise exposure. American Journal of Otolaryngology, 15(1), 26-32.

11. Kopke, R., Allen, K.A., Henderson, D., Hoffer, M., Frenz, D., Van de Water, T. (1999) A radical Demise: Toxins and trauma share common pathways in hair cell death. Annals of the New York Academy of Sciences, 28, 171-191.

12. Prince, M.M., Stayner, L.T., Smith, R.J., Gilbert, S.J. (1997). A re-examination of risk estimates from the Niosh Occupational Noise and Hearing Survey (ONHS). The Journal of the Acoustical Society of America, 101(2), 950-963.

13. Smoorenburg, G.F. (1992). Speech reception in quiet and in noisy conditions by individuals with noise-induced hearing loss in relation to their tone audiogram. The Journal of the Acoustical Society of America, 91(1), 421-437.

14.Meyer-Bisch, C. (1996). Epidemiology evaluation of hearing damage related to strongly amplified music (personal cassette players, discotheques, rock concerts)-high-definition audiometric survey on 1364 subjects. Audiology, 35(3), 121-142.

15. The League of Hard of Hearing. (2001). [Noise tour of cities around the United States.] www.lhh.org

16. Wallhagen, M.I., Strawbridge, W.J., Cohen, R.D., Kaplan, G.A. (1997) An increasing prevalence of hearing impairment and associated risk factors over three decades of the Alameda County Study. American Journal of Public Health 87(3), 440-442.

17. Dalton, D.S., Cruickshanks, K.J., Wiley, T.L., Klein, B.E.K., Klein, R., Tweed, T.S. (2001). Association of leisure-time noise exposure and hearing loss. Audiology, 40(1), 1-9.

18. Niskar, A.S., Kieszak, M.A., Holmes, A.E., Esteban E., Rubin C., Brody D.J. (July 2001). Estimated prevalence of noise-induced hearing threshold shifts among children 6 to 19 years of age: The third national health and nutrition examination survey, 1988-1994, United States. Pediatrics, 108(1), 40-43.

The Center for the Advancement of Health is an independent nonprofit organization that promotes greater recognition of how psychological, social, behavioral, economic and environmental factors influence health and illness. The Center advocates the highest quality research and communicates it to the medical community and the public. The fundamental aim of the Center is to translate into policy and practice the growing body of evidence that can lead to the improvement and maintenance of the health of individuals and the public. The Center was founded by the John D. and Catherine T. MacArthur Foundation and the Nathan Cummings Foundation, which continue to provide core funding. Funding for this series was provided by the Robert Wood Johnson Foundation.

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