Abstract
The hypothesis was advanced in previous papers that the symptoms of multiple chemical sensitivity (MCS) are due to the presence of thresholds, or increases in thresholds, in detoxication processes, so that these are not activated by low exposures to xenobiotic chemicals. Here the argument is taken further forward, to propose that thresholds for the induction of the enzymes which mediate the biotransformation of xenobiotics, and the elevation of those thresholds above normal levels, are the basic parameters giving rise to the symptoms of MCS. Some theoretical and experimental evidence is quoted to support the existence of these thresholds, and examples are given of how many of the characteristics of MCS can be expected to follow from the application of these ideas, which do not conflict with orthodox toxicology.