Clinical Review Abc Of Allergies ABC of allergies

Allergy and the skin. I—Urticaria

BMJ 1998; 316 doi: (Published 11 April 1998) Cite this as: BMJ 1998;316:1147
  1. Malcolm W Greaves,
  2. Ruth A Sabroe

    Acute urticaria

    Episodes of acute urticaria are common. Causes include type 1 hypersensitivity reactions to certain foods and drugs, including blood products. In up to 50% of cases a cause is not identified. The involvement of a particular food allergen can be confirmed by the radioallergosorbent test (RAST) and skin prick tests. Allergy to latex usually manifests as contact urticaria or with systemic symptoms but rarely presents with generalised urticaria. As with suspected reactions to peanuts it is recommended that tests for latex allergy be done in a hospital setting as severe systemic reactions may occur. Management of acute urticaria includes avoidance of the causative agent and treatment with H1 antihistamines. A short course of prednisolone can be given for severe episodes of urticaria unresponsive to antihistamines.

    Causes of acute urticaria

    • Idiopathic origin

    • Food: fruits (for example, strawberries), seafood, nuts, dairy products, spices, tea, chocolate

    • Drugs: antibiotics (for example, penicillin) and sulphonamides; aspirin and non steroidal anti inflammatory drugs; morphine and codeine

    • Blood products

    • Viral infections and febrile illnesses

    • Radio contrast media

    • Wasp or bee stings

    Chronic urticaria

    Chronic urticaria is conventionally defined as the occurrence of daily or almost daily widespread itchy weals for at least six weeks. It occurs in at least 0.1% of the population and is much more troublesome than acute urticaria. Recent studies using an internationally recognised quality of life questionnaire, the Nottingham health profile, have highlighted the serious disability of patients with chronic urticaria, including loss of sleep and energy, social isolation, altered emotional reactions, and difficulties in aspects of daily living. The disability is of the same order as that experienced by patients with severe chronic ischaemic heart disease.

    Dermographism induced with a calibrated, spring loaded dermographometer

    Physical urticarias

    The first step is to identify patients with physical urticarias. These are patients in whom wealing and itching is provoked at the sites …

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