Allergy and Allergic Diseases

From the Imperial College School of Medicine, National Heart and Lung Institute, London. LLERGIC rhinitis, asthma, and atopic eczema are among the commonest causes of chronic ill health. These diseases are increasing in prevalence, and they add considerably to the burden of health care costs. In Sweden, for example, the number of children with allergic rhinitis, asthma, or eczema roughly doubled over a 12-year period, 1 and in the United States the annual cost of treating asthma is about $6 billion. 2 The term “allergy” was introduced in 1906 by von Pirquet, who recognized that in both protective immunity and hypersensitivity reactions, antigens had induced changes in reactivity. 3 With the passage of time the word has become corrupted and is now frequently used synonymously with IgE-mediated allergic disease. It was von Pirquet’s intent that the term should apply to the “uncommitted” biologic response, which may lead either to immunity (a beneficial effect) or allergic disease (a harmful effect). The term “atopy” (from the Greek atopos, meaning out of place) is often used to describe IgE-mediated diseases. Persons with atopy have a hereditary predisposition to produce IgE antibodies against common environmental allergens and have one or more atopic diseases (i.e., allergic rhinitis, asthma, and atopic eczema). Some allergic diseases, such as contact dermatitis and hypersensitivity pneumonitis, develop through IgE-independent mechanisms and in this sense can be considered nonatopic allergic conditions. This article reviews the basis of atopic allergy, the diseases with which it is associated, and approaches to treatment.