Number of people attribute symptoms to everyday environmental exposures at levels that are well below those known to cause adverse health effects and that are tolerated by the majority. Intolerance may develop to various environmental factors, typically to odorous chemicals, but also to non-perceivable factors considered potentially harmful to health, e.g. electrical devices. Reactions due to intolerance range from unpleasant sensations or annoyance to disabling symptoms, which may lead to serious restrictions in daily life. Reactions often initiate exposure assessments in work, home or public environment and may lead to excessive actions to eliminate minor exposures.
In 1996, the WHO classified all medically unexplained conditions attributed to different environmental exposures under the term idiopathic environmental intolerance (IEI), regardless of the factor in question (IPCS 1996). The factors may include e.g chemicals, moulds. The term is most commonly used for multiple chemical sensitivity (MCS), but also nonspecific building-related symptoms (or sick building syndrome), hypersensitivity to electromagnetic fields (EMFs) are regarded as its subtypes. Although the various types of environmental intolerance (EI) share common core characteristics, there is no generally agreed definition of the condition.
The prevalence estimates are based on self-reporting. In adults, the prevalence estimates of EI attributed to chemicals vary from 9% to 52%, to EMFs from 1.5% to 21%, and to sounds from 8% to 39% (Karvala, et al 2017, submitted).
Environmental intolerance manifests as different degrees of annoyance, which shows a continuum with increasing symptoms, behavioural changes and disability.
IPCS/WHO (1996). Conclusions and recommendations of a workshop on Multiple Chemical Sensitivities (MCS). International Program on Chemical Safety/World Health Organisation. Regul Toxicol Pharmacol 24:188–189.