Atypical Human Responses To Low‐Level Environmental Contaminants: the Problem of Multiple Chemical Sensitivities
Authors: Cullen Mark R. 
Published: August 2005

Abstract
Fundamental shifts in the nature of work, changing composition of the workforce, and changes in societal perceptions about health have brought to the practice of occupational medicine some new areas of focus. Where once one could be content with a clear understanding of the impact of chemical and physical hazards at the doses which caused clinically apparent illness or injury, primarily in manufacturing, mining, agriculture and construction, there has been a rapid increase in concern about the impacts of many of these same hazards as they arise in the nonindustrial setting, impacting far larger numbers of workers who often bring very different experiences and expectations regarding health in the workplace. Even in the industrial settings, the introduction of effective controls—which have markedly reduced, at least in developed countries, the well understood classic occupational diseases and risks—have had as an unexpected consequence a refocusing of attention from the devastating consequences of exposures above established Threshhold Limit Values (TLV's) or occupational exposure limits, onto the possibility of effects occurring at lower levels, confidently deemed safe by comparison to the “old” context of practice when the major hazards were still extant and uncontrolled.
There are a variety of reasons why existing estimates of thresholds may be inadequate for predicting what could be anticipated when large populations are exposed to various hazards at low levels and these are discussed.
The workers at potential risk for exposure are no longer the “rugged” men who comprised much of the workforce of previous eras, but are now men and women who have never worked in what most occupational health professionals would call a dangerous workplace, and have no particular reference to historic risks by which to be assuaged or reassured that things are now safe. People are far more medically aware and sophisticated as well, and no longer consider a little mucosal irritation or muskulo‐skeletal pain as “normal”. These “effects” are likely to be perceived, with or without toxicologic substantiation, as evidences of clinical illness or injury, possibly even serious, especially if they occur more noticeably in the workplace than without. Such complaints, which in a former world may never have received medical attention, are now the basis for frequent visits, inquiry, and not rarely request for the professional services of occupational health and safety specialists.
The burgeoning experience with these issues has become the basis for some important new scientific inquiry in the domain of indoor air quality, and has been extensively reviewed in this work.
Some individuals in these buildings as well as in other work‐place and nonworkplace settings, are apparently responding unpredictably. Unlike workers in the outbreaks described by Morey (Chapt. 69), such individuals may “react” to chemicals in widely diverse settings, their symptoms may be more extensive and profound, and they do not necessarily respond to control measures which are typically effective despite our imperfect understanding of why. It is to this increasingly recognized problem, often referred to as Multiple Chemical Sensitivities (MCS), that this chapter is devoted.
Since this chapter is premised on the assessment which occurs as a result of the complaints of individual or groups of workers in setting where complaints would not traditionally be anticipated, Three case examples to illustrate the kinds of issues which arise are given. This is followed by a detailed delineation of the differential possibilities which must be considered when such cases arise. Current theories about the pathogenesis, and our present understanding of the clinical course and epidemiology of MCS will be followed by sections on management from the hygiene and medical perspectives.