Table 1: Proposed Definitions for Multiple Chemical Sensitivity (MCS) since 1985.

1985   ad hoc Committee, Ontario Ministry of Health:
More than 3 months duration
Multisystem disorder
Intolerance to foods, chemicals, environmental agents at levels generally tolerated by majority
No objective physical findings; no consistently altered laboratory test
Symptoms diminish with avoidance; recur with exposure.
1987   Cullen:
Multiple chemical sensitivities is an acquired disorder characterized by recurrent symptoms, referable to multiple organ systems, occurring in response to demonstrable exposure to many chemically unrelated compounds at doses far below those established in the general population to cause harmful effects. No single widely accepted test of physiologic function can be shown to correlate with symptoms.
1991   Ashford and Miller:
The patient with multiple chemical sensitivities can be discovered by removal from the suspected offending agents and by rechallenge, after an appropriate interval, under strictly controlled environmental conditions. Causality is inferred by the clearing of symptoms with removal from the offending environment and recurrence of symptoms with specific challenge.
1992   American Academy of Environmental Medicine:
Ecologic illness is a chronic multi-system disorder, usually polysymptomatic, caused by adverse reactions to environmental incitants, modified by individual susceptibility and specific adaptation. The incitants are present in air, water, food, drugs, and our habitat.
1992 National Research Council (NRC), Workshop on Multiple Chemical Sensitivities, Working Group on Research Protocol for Clinical Evaluation:

Symptoms or signs related to chemical exposures at levels tolerated by the population at large that are distinct from such well recognized hypersensitivity phenomena as IgE-mediated immediate hypersensitivity reactions, contact dermatitis, and hypersensitivity pneumonitis.

Sensitivity may be expressed as symptoms and signs in one or more organ systems

Symptoms and signs wax and wane with exposures.

It is not necessary to identify a chemical exposure associated with the onset of the condition.
Preexistent or concurrent conditions ( e.g., asthma, arthritis, somatization disorder, or depression) should not exclude patients from consideration.

1992   Association of Occupational and Environmental Clinics: Workshop on Multiple Chemical Sensitivity, Working Group on Characterizing Patients:
A change in health status identified by the patient
Symptoms triggered regularly by multiple stimuli
Symptoms experienced for at least 6 months
A defined set of symptoms reported by patients
Symptoms that occur in three or more organ systems|

Exclusion of patients with other medical conditions (psychiatric conditions are not considered exclusionary).

1993   Nethercott et al.:
The symptoms are reproducible with exposure.
The condition is chronic.
Low-level exposure results in manifestations of syndrome.

Symptoms improve or resolve when incitants are removed.

Responses occur to multiple, chemically unrelated substances.

1995   Kurt:
The symptoms are "odor-triggered" and "exposure perceived" at very low levels, but are manifest as a multitude of neurobehavioral symptoms that correspond to the accepted definitions of panic disorder.
1996   International Program on Chemical Safety (IPCS):
An acquired disorder with multiple recurrent symptoms; associated with diverse environmental factors tolerated by the majority of people; not explained by any known medical or psychiatric disorders.

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