The psychogenic theory presupposes that idiopathic environmental intolerance (IEI) is an overvalued idea explained by psychological and psychosocial processes. The polysomatic symptoms are amplifications of complaints common to the general population, psychophysiological manifestations of stress and the stress-response, or symptoms of psychiatric clinical syndromes. The psychogenic theory is supported by provocation challenge studies which demonstrate that appraisals of 'reactions' are unreliable and cognitively mediated. Clinical studies of IEI cases consistently identify greater incidence of current and premorbid lifetime psychiatric disorders and co-morbidity with functional somatic syndromes that are fashionable 'diagnoses'. The toxicogenic theory presupposes low-level chemical sensitivity or intolerance without objective signs to a plethora of diverse chemical agents. Symptoms are synonymous with disease and attributions are synonymous with cause. Hypotheses about physiological processes and mechanisms are implausible and unsupported by evidence. Advocates claim this phenomenon is so ephemeral that the principles and methods of toxicology do not apply and that a scientific paradigm shift is in order.