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Contact urticaria is mediated by either allergic or nonallergic mechanisms. Allergic contact urticaria is mediated by IgE, and affected patients are usually atopic. Contact urticaria may be confused with allergic contact dermatitis when the erythematous wheals evolve into a vesicular dermatitis. However, the clinical history will reveal that the patient with contact urticaria developed itching at the time or soon after contact. [Rosenstock, p. 709] Contact urticaria is an effervescent swelling and erythema of the skin (wheal and flare) without scaling or other changes in the epidermis. Systemic symptoms are rarely associated with contact urticaria. High-risk occupations are food handlers, bakers, healthcare workers, pharmaceutical workers, animal handlers, gardeners, florists, woodworkers, and farmworkers. [Asthma in the Workplace, p. 804-9] Some patients with contact urticaria have both immediate and delayed reactions. Other patients develop life-threatening anaphylactic reactions. IgE mediated contact urticaria is caused by the hair, urine, and saliva of animals and by latex, biocides, and some fruits and vegetables. Protein contact urticaria is an unusual type of contact urticaria that has been described in sandwich makers and other food workers who develop immediate itching, stinging, and vesiculation within minutes of handling meat or fish. [Marks, p. 310-11] Nonallergic on nonimmunologic contact urticaria (NICU) is more common than the allergic type. The most common causes of NICU in the workplace are the preservatives, flavorings, and fragrances added to food, cosmetics, and drugs. NICU occurs in most or all of exposed workers. Allergic contact urticaria is most common among food processors, especially in those handling food-derived protein allergens. Natural rubber latex contact urticaria is an example of the allergic type. Latex allergy prevalence among healthcare workers in different countries varies from 3% to 16%. [Kanerva 2004, p. 95-7] Most reported cases of occupational contact urticaria are immunologic. Some low-molecular-weight chemicals rarely cause occupational contact urticaria: anhydrides, epoxy resins, polyfunctional aziridines, nickel, and reactive dyes. [Reference Link] |
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