Stephen Stansfeld, MBBS, MRCP, MRCPsych, PhD

"Noise" is generally defined asunwanted sound and is perceivedas a pollutant and anenvironmental stressor. As opposed tosound, noise involves a significantpsychological component in additionto the physical component of soundperceived by the ear and transmittedby the auditory nerve to the temporallobe in the brain.

Typically, sound is described in termsof its intensity or sound pressure level,its frequency, periodicity, and duration.Sound pressure level is measured indecibels (dB). Since the human earresponds differently to different frequencyranges, filter meters that workmore like the human ear are often usedto measure sound pressure levels; insuch cases, the unit is described asdBA, which means that a weightedfilter was used.

Sound is also described in terms ofequivalent sound levels (Leq), measurementsthat address average noiselevels of fluctuating noises. Other characteristics,such as the predictability ofthe noise, its meaning, and the degree ofpersonal control over noise, may influinfluencepeople's responses. The 

 listscommon noises and their sound levels.

Grand Canyon at night (birds, wind, no roads)

Adapted from Noise Pollution Clearinghouse
  (available at: 

http://www.nonoise.org/library/  household/index.htm

Exposure to environmental noise,including transport, construction, andindustry noise, is increasing. While theintensity of noise from aircraft and carsmay have diminished, the frequency ofnoise events seems to have increasedin recent years, and the amount of theday without noise has lessened.

There are several ways in which people'severyday functioning is disturbed byexposure to noise. The most widespreadresponse to noise is annoyance; thisincludes elements of fear, mild anger,and a belief of being avoidably harmed.

Reactions of annoyance are often associatedwith the degree of interferencethat noise causes in everyday activities.Dose-response relationships betweenthe intensity of noise and annoyancefrom air, road, and rail transport havebeen found in a number of studies.

Severe annoyance typically beginsabove 50 dBA to 55 dBA Leq.

Exposure to noise during sleep hasbeen related to difficulties in getting tosleep, changes in sleep stages, andawakenings.

 While effects of noiseexposure on sleep are evident in laboratorystudies, these effects are moredifficult to demonstrate in communitystudies, where residents may habituateto prolonged noise exposure.

 There isno evidence that noise exposure, throughinsomnia, triggers depressive illness, althoughthis pathway seems plausible.

There is also limited evidence ofnoise affecting pathophysiology, apartfrom the issue of noise-induced hearingloss. In occupational settings, forinstance, there is evidence of raisedlevels of catecholamines and cortisol inpersons exposed to very high levels ofnoise, typically above 80 dBA.

Although the evidence is less convincing,there are some data that showhormonal responses in relation to environmentalnoise. There is also someevidence that aircraft and road trafficnoise, typically at levels greater than65 dBA to 70 dBA Leq, is related to asmall increased risk of hypertension andcoronary heart disease.

An important area of the consequencesof noise relates to task performance.Laboratory studies have shown thatnoise exposure increases arousal andcan improve cognitive performance onsimple tasks that require vigilance. Onthe other hand, noise can interfere with more complex tasks, decreasing attentionas well as altering choice of taskstrategy.

In the so-called irrelevant speecheffect, cognitive performance can bedisturbed when the individual hearsbackground speech that is irrelevant tothe task; it is believed that this may interferewith memory processes.

 Thisphenomenon has obvious implications forpeople working in open-plan offices.

Recent epidemiologic studies ofschoolchildren have found that aircraftnoise exposure at school was associatedin a linear exposure-effect relationshipwith impairment of reading andmemory recognition,

 The mechanism for thisis uncertain; it may relate to disturbancesin communication between teachersand pupils or maladaptive attentionalstrategies.

Because of its effects on annoyance,sleep, and cognitive performance, noisemight be expected to affect mentalhealth. Although there is some evidenceof this effect, the data are by no meansclear-cut.

At the simplest level, noise exposurein the community has been related toan increased incidence of psychologicalsymptoms, including headaches,anxiety, fatigue, and depression.

Early studies of mental hospital admissionsand aircraft noise exposure showeda mixed picture,

 and communitysurveys, which are a more appropriatedesign for detecting the effects of environmentalnoise, have only shown effectsin certain subgroups.

Two epidemiologic studies of roadtraffic noise have found associationsbetween noise exposure and symptomsof mental distress

 examined persons living closeto an airport and matched them withcontrols. Researchers found a higherprevalence of generalized anxiety disorder,as diagnosed by the CompositeInternational Diagnostic Interview, among those exposed to high levels ofaircraft noise than among people livingin quieter areas.

Relationships between militaryaircraft noise exposure and psychologicaldistress have been found in a rangeof Japanese studies, suggesting theremay be more evidence for effects onmental health at higher noise levels.Increased levels of prescriptions ofhypnotics and nonprescription sedativesin areas exposed to aircraft noise(compared with those in quieter areas)can be considered indirect evidence ofthe mental health effects of noise.

Thus, there is a need for more researchto provide additional insight and perhapsstronger evidence for the link betweennoise and psychological distress. Itshould be noted that noisy environmentsare often socioeconomically disadvantagedenvironments, and it is difficult todisentangle the effect of noise on mentalhealth from the effects of other stressors,both social and environmental, thatmay be present.

Noise from neighbors has received littleresearch investigation but may come tothe attention of psychiatrists. In theUnited Kingdom, this is the mostcommon source of noise complaints tolocal government authorities.

Noise that is continuous, apparentlyindefinite, of uncertain cause or source,emotive or frightening, or apparentlydue to thoughtlessness or lack of considerationis most likely to elicit an adversereaction.

In some cases, on further inquiry, itbecomes apparent that complaints ofnoise disturbance are related to persecutorydelusions and may be a symptomof psychosis. In these cases, whichoften come to the attention of psychiatrists,the disturbances are typically partof a wider system of persecutory ideasabout neighbors, in which noise is onlyone of many afflictions that the patientbelieves the neighbors are causing him or her. Here, the management relates tothe primary underlying illness, for whichrisk assessment (including assessmentof the risk of aggression against neighbors)will be important. On the otherhand, the clinician should not be tooready to dismiss the reality of the noisecomplaints.

Prolonged exposure to noise can bevery upsetting and intrusive and caninterfere with sleep and everyday activities,especially in poorly built dwellings,where even low-intensity noisesfrom neighbors may be clearly audible.This may be a problem particularlyamong people who are chronicallyanxious and who complain of sensitivityto noise (ie, prolonged noiseexposure may make them more anxiousand unhappy).

There may be a phobic reaction tonoise in some people with noise sensitivitythat might respond to a cognitivebehavioralapproach.

 There isevidence that people with existingdepression and anxiety are more likelyto be sensitive to the effects of noise.

Perceptions of lack of control overthe noise, unpleasant meanings associatedwith the noise, or a feeling thatothers don't care may exacerbate negativeresponses. Active coping strategies,such as shutting windows, spending moretime in the most quiet areas of their residence,and complaining to the relevantauthorities, may reduce negative responsesto noise. Conversely, passive copingis likely to aggravate noise effects.

Current evidence suggests that environmentalnoise exposure, especially athigher levels, is related to mental healthsymptoms and possibly to increasedanxiety and consumption of sedativemedication. Although noise exposuremay be responsible for only relativelymild psychiatric disorders, it doesinvolve large numbers of people whosequality of life may be impaired significantly.For the fifth of the populationwho are sensitive to noise, chronic noiseexposure can cause considerable disturbanceand misery.

Dr Stansfeld is professor of psychiatry at theCentre for Psychiatry, Wolfson Institute ofPreventive Medicine, Barts, and The LondonQueen Mary's School of Medicine andDentistry, London. He is also secretary of theInternational Commission on the BiologicalEffects of Noise and has a long-standing interestin research on noise and health.

Dr Stansfeld is a consultant on a project onnoise and vibration impact assessment sponsoredby the United Kingdom Department ofEnvironment.

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Articles

Noise, or unwanted sound, is a pollutant and an environmental stressor. The frequency of noise events seems to have increased in recent years while the amount of the day without noise has lessened.

Stephen Stansfeld, MBBS, MRCP, MRCPsych, PhD

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