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The psychology of multiple allergy.

Many people present to their doctors with multiple unexplained symptoms which they attribute to allergy. Such subjects develop symptoms in response to many substances including foods and chemicals and therefore avoid contact with them. Epidemiological research has confirmed the large discrepancy between self perception of allergy among the public and its detection by objective methods. For example, in a study of30 000 people in High Wycombe a 7% prevalence of perceived allergy to food additives was found, whereas the prevalence of reactions detected by double blind challenge (the definitive test) was only 0 023%.' Those at the extreme end of this range often attract a diagnosis of total allergy syndrome, multiple chemical sensitivity, or environmental illness-diagnoses that most allergists or immunologists repeatedly reject.23 These patients have no consistent physical or immunological abnormalities.45 The failure of conventional allergic mechanisms to explain symptoms has led to suggestions that, although these patients do not exhibit allergic mechanisms, they have ill understood intolerances or sensitivities.6 When patients are tested by double blind challenges, however, few react consistently to the substances in question.78 If the problem is not one of allergy then what are the possible causes? Research has shown the relevance of psychological disorder.89 Black and colleagues found that 17 of 26 patients (65%) who believed that they had the total allergy syndrome fulfilled criteria for current or past mood, anxiety, or somatoform disorders, compared with only 28% of controls matched for age and sex.'0 Other diagnoses have been reported, including schizophrenia in patients with the total allergy syndrome,9 the hyperventilation syndrome in patients with alleged food allergy,7 anorexia nervosa in multiple food hypersensitivity," and post traumatic stress disorder in patients with multiple chemical sensitivity.'2 A perusal of the vast self help literature yields descriptions of sufferers whose case histories raise the possibility of serious psychiatric illness. But the exact role of psychiatric disorder remains to be established. Some researchers have not used standardised interviews or diagnostic criteria. Studies have included patients who agreed to some form ofpsychological assessment either through a liaison psychiatry service or for compensation claims. Controls have not been drawn from populations of similarly chronically ill patients hence such studies cannot answer questions about the direction of causality. A recent study that avoided these pitfalls, however, confirmed that whereas immunological abnormalities were notably absent, psychological symptoms were a central component ofchemical sensitivity.' Nevertheless, the high prevalence of psychiatric disorder suggests that psychological factors must be relevant. A history of psychiatric morbidity predating exposure to chemicals in the workplace and the onset of sensitivity to chemicals has been found to predict the development of multiple chemical sensitivity,8 as has the number of prior medically unexplained symptoms.58 Brodsky reviewed the medical records of eight patients with the total allergy syndrome and found that all had longstanding psychological problems and a history of somatic symptoms years before their exposure to offending substances at work.'3