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The nostril membrane is so irritable that light dust, contradiction, an absurd remark—anything—sets me sneezing and I can be heard in Taunton with a favourable wind, a distance of six miles. Turn your mind to this little curse. If consumption is too powerful for physicians, at least they should not suffer themselves to be outwitted by such little upstart disorders as the hay fever.
SYDNEY SMITH, LETTER TO DR HOLLAND, 1835
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Allergic disorders affect approximately 20% of the population. The clinical spectrum of allergic disorders includes asthma, rhinitis, atopic dermatitis, drug allergy, food allergy, insect sting allergy and anaphylaxis.1 The most common allergies are those associated with IgE-mediated (immediate or type 1) hypersensitivity, such as allergic rhinoconjunctivitis (hay fever), atopic dermatitis (eczema) and allergic asthma.2
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Less commonly encountered but of increasing clinical importance in the community are IgE-mediated allergies to foods such as peanuts and/or other nuts and seafoods (crustaceans or molluscs), which may cause urticaria, angioedema, anaphylaxis and even death. Peanuts are one of the most common causes of food-induced anaphylaxis in adults. A clinically significant cross-reactivity between peanuts and other legumes is uncommon, but allergy to tree nuts such as almonds and walnuts may occur in up to 50% of those with peanut allergy.1 Another special case is the oral allergy syndrome, in which people with some degree of seasonal allergy to grass pollens or birch pollen suffer oral itch and swelling when they come into contact with certain fruits. This problem may be alleviated by desensitisation to pollens.1
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Natural rubber latex allergy is an increasingly important cause of type 1 hypersensitivity, affecting particularly medical and paramedical personnel, and patients who have had multiple operations or procedures. Diagnosis is suggested by history and confirmed by specific skin tests or the detection of serum-specific IgE. The development of urticaria on contact with latex is highly suggestive of underlying type 1 hypersensitivity. An interesting association between latex allergy and sensitivity to fruit occurs most commonly with banana, kiwifruit or avocado.1
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Atopy occurs in those 45% of the population who have an inherited tendency for an exaggerated IgE antibody response to common environmental antigens.2 It is not a disease in itself. There will be a positive response to one or more allergen skin-prick tests and usually a family history of allergic disorders. Of those who are atopic, one-half to one-third manifest an allergic disorder, most commonly allergic rhinitis, asthma, atopic dermatitis or allergic gastroenteropathy.
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COMMON ALLERGENS CAUSING IMMEDIATE HYPERSENSITIVITY
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It is helpful to consider important allergen exposure during history taking. TABLE 72.1 lists sources of common allergens.
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