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Am Fam Physician. 2000;61(11):3408

Allergic contact dermatitis is most commonly caused by poison ivy, western poison oak, eastern poison oak and poison sumac. Urushiol, commonly the chief allergen, is found in the oleoresinous sap located in the leaves, stems and roots of these plants. Between 50 and 70 percent of people are sensitive to contact with the oleoresin released from a bruised plant. Indirect contact through clothing, pets and even smoke from a burning plant may cause a similar reaction. Lee and Arriola review common presenting signs and symptoms, and management and prevention strategies for allergic contact dermatitis caused by plants.

The rash associated with contact dermatitis typically appears 24 to 48 hours after exposure in a previously sensitized person. This rash is usually self-limiting and resolves one to two weeks after exposure. Redness and intense pruritus also develop, followed by papules, vesicles and sometimes bullae. Lesions can appear in streaks, suggesting plant contact. Fluid from the lesions is not sensitizing to others. Complications include secondary bacterial infections and, rarely, erythema multiforme and urticaria.

Management should include thorough washing with soap and water, preferably within 10 minutes of exposure, as this may prevent dermatitis. All contaminated clothes should be removed as soon as possible and cleaned. Frequent baths, using colloidal oatmeal, also relieve symptoms. Treatment of mild to moderate rash includes application of cool compresses or diluted aluminum acetate solution, such as Burow's solution, or calamine lotion. Use of topical antihistamines and anesthetics should be avoided because of the possibility of increased sensitization. Early application of topical steroids is useful to limit erythema and pruritus. However, occlusive dressings should be avoided on moist lesions. Refractory dermatitis can be treated with oral corticosteroids such as prednisone, with an initial dosage of 1 mg per kg per day, slowly tapering the dosage over two to three weeks. Shorter courses of steroids may be followed by severe rebound exacerbations shortly after drug therapy is discontinued. Oral antihistamines may help reduce pruritus and provide sedation, when needed.

The authors conclude that prevention requires educating patients to recognize the offending plants and to wear protective clothing when engaging in outdoor activities. Desensitization efforts are of uncertain value. The success of topical barrier preparations is variable, but some, such as organoclay preparation, can limit response in exposed susceptible persons when applied to the skin at least 15 minutes before anticipated exposure. Application should be repeated every four hours if exposure is prolonged.

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