Multiple Chemical Sensitivity (MCS) is not recognised as an allergy in the true medical sense, as most reactions are not mediated by the IgE antibody. Symptoms can occur in many different organ systems as well as affect the central nervous system.
Several tests have been proposed to confirm or refute diagnosis but none have yet proved entirely satisfactory. Due to the subjective and varying nature of the illness, standard medical investigations often remain inconclusive and it is common for MCS sufferers to find blood test results returned as 'normal'. In consequence, GPs vary widely in their treatment and ongoing support for patients. A large percentage of doctors continue to dismiss the condition as a psychological complaint or psychiatric disease, despite increasing medical evidence to the contrary.
In 1989, a group of 89 doctors, scientists and researchers specialising in MCS met in the US to propose a standardised clinical definition. A sixth criterion was added in 1999. Since then, none of the six guidelines have been opposed in published medical literature and although these criteria have not yet been accepted as standardised clinical guidelines, they have been accepted by most international scientists as a basis for common understanding.
The criteria are as follows: The condition is chronic. The symptoms can be reproduced by repeated chemical exposure. Low levels of exposure [lower than previously or commonly tolerated] result in manifestations of the syndrome. Responses occur to multiple chemically unrelated substances. The symptoms improve or resolve when the incitants are removed. Symptoms occur in multiple organ systems.
The working group recommended that "MCS be diagnosed whenever all 6 of the consensus criteria are met, along with any other disorders that also may be present, such as asthma, allergy, migraine, chronic fatigue syndrome (CFS), and fibromyalgia (FM). MCS should be excluded only if a single other multi-organ disorder can account for both the entire spectrum of signs and symptoms and their association with chemical exposures, such as mastocytosis or porphyria, but not CFS or FM, which are not so associated." (Multiple Chemical Sensitivity: A 1999 Consensus, in Archives of Environmental Health, May/June 1999, Vol. 54, No. 3)
To assist doctors in making a diagnosis, the group also recommended the following:
- Approved screening questionnaires
- A list of overlapping disorders to consider in the differential diagnosis of MCS
- A list of clinical signs and abnormal values from clinical-chemical parameters (published in peer-reviewed literature) even though they are not commonly accepted as biomarkers for MCS
- Following up on all MCS cases using qualitative and quantitative methods
Since then several diagnostic questionnaires have been published, but none are routinely used.
The 1999 report remarked:
"The millions of civilians and tens of thousands of Gulf War veterans who suffer from chemical sensitivity should not be kept waiting any longer for a standardised diagnosis while medical research continues to investigate the aetiology [cause] of their signs and symptoms."