Multiple chemical sensitivity

Of the 200 or so recent publications on MCS in the biomedical literature, only about 30 relate to original research. In almost all cases, the validity and precision of the research leave much to be desired. This is related to the fact that there is no unambiguous definition of MCS, and hence, a priori, there is considerable vagueness concerning both the possible causes and effects of the phenomenon. If MCS is to be researched in a more scientific manner, there is need for hypotheses that are both reasonable and testable (Dye97). Researchers should agree on the measurable characteristics of MCS, as well as its possible causes. Because these are failing provocative research to determine the nature and causes of sensitivity in people with MCS complaints is without meaning and standardised research into possible ways of preventing the phenomenon is not possible.

Non-specific health complaints such as fatigue, concentration problems, headaches, respiratory difficulties and sore throat occur with great frequency. Clearly, these complaints deserve the attention of the healthcare services, some of whose members see a connection with exposure to chemicals. The issue at present is how far the current state of scientific knowledge justifies making such a connection, and whether people with the complaints benefit from a diagnosis of multiple chemical sensitivity.

To label an environmental factor as the cause of a health problem, well-defined criteria need to be satisfied (see Hil65 and McC97 for example). The relation between the supposed cause and the health problem must be consistent and specific and the pathology must be seen to develop at an identifiable point in time between exposure and occurrence of the complaints. The existence of a dose-response relation is important, and the complaints must be biologically plausible. The degree of plausibility depends on the state of science. Observations should be coherent, and confirmed with positive and negative checks. Analogies strengthen the likelihood of a causal connection.

In the publications on complaints ascribed to MCS, these criteria have not been met. The relation between exposure to chemical substances and reported non-specific health problems is at best only associative. The existence of a clinically identifiable disorder, based on a reproducible mechanism, has not been proved. However, it is a fact that all kinds of environmental factors can cause different reactions in different people: one person can tolerate a factor without any problems; another experiences health complaints. Various factors and mechanisms play a role in this. People with the complaints, however, enjoy no benefit from all these types of phenomena being lumped together under a single label. A single label can confuse the situation, and makes it difficult to introduce appropriate environmental measures or treat the individual in question.

The conclusion has to be that current knowledge provides no medical scientific justification for the existence of multiple chemical sensitivity as a syndrome or disease. This conclusion does not reduce the importance of the assessment of the possible relations between combined exposures and the occurrence of health complaints.