Health effects caused by noise: evidence in the literature from the past 25 years.

Traffic noise is the most important source of environmental annoyance. According to the Environmental Expert Council of Germany, severe annoyance persistent over prolonged periods of time is to be regarded as causing distress. Previously, extraaural noise effects were mostly assessed using a paradigm in which the sound level played the major role. On the basis of this paradigm the relatively low sound level of environmental noise was not considered to be a potential danger to health. In contrast to this numerous empirical results have shown long-term noise-induced health risks. Therefore a radical change of attitude - a change of paradigm - is necessary. For an immediate triggering of protective reactions (fight/flight or defeat reactions) the information conveyed by noise is very often more relevant than the sound level. It was shown recently that the first and fastest signal detection is mediated by a subcortical area - the amygdala. For this reason even during sleep the noise from aeroplanes or heavy goods vehicles may be categorised as danger signals and induce the release of stress hormones. In accordance with the noise stress hypothesis chronic stress hormone dysregulations as well as increases of established endogenous risk factors of ischaemic heart diseases have been observed under long-term environmental noise exposure. Therefore, an increased risk of myocardial infarction is to be expected. The results of individual studies on this subject in most cases do not reach statistical significance. However, according to the Environmental Expert Council, these studies show a consistent trend towards an increased cardiovascular risk if the daytime immission level exceeds 65 dB(A). Most of the previous studies on the extraaural effects of occupational noise have been invalidated by exposure misclassifications. In future studies on health effects of noise a correct exposure assessment is one of the most important preconditions.