CAUSES
. Plants
. Rhus-urushiol (poison ivy, oak, sumac)
. Primary contact - plant (roots/stems/leaves)
. Secondary contact - clothes/fi ngernails (not blister fluid)
. Chemicals
. Nickel - jewelry, zippers, hooks, watches
. Potassium dichromate - tanning agent in leather
. Paraphenylenediamine - hair dyes, fur dyes, industrial chemicals
. Turpentine - cleaning agents, polishes, waxes
. Soaps, detergents
. Topical medicines
. Neomycin - topical antibiotics
. Thimerosal (Merthiolate) - preservative in topical medications
. Anesthetics - benzocaine
. Parabens - preservative in topical medications
. Formalin - cosmetics, shampoos, nail enamel
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DIFFERENTIAL DIAGNOSIS :
β’ Based on clinical impression - appearance, periodicity, localization
β’ Groups of vesicles - herpes simplex
β’ Diffuse bullous or vesicular lesions - bullous pemphigoid
β’ Photo-distribution - phototoxic/allergic reaction to systemic allergen
β’ Eyelids - seborrheic dermatitis
β’ Scaly eczematous lesions - atopic dermatitis, nummular eczema, lichen simplex chronicus, stasis dermatitis, xerosis
SPECIAL TESTS Patch tests for allergic contact dermatitis (systemic corticosteroids or recent, aggressive use of topical steroids may alter results)