Allergic contact rashes are caused when your skin reacts to allergens. These allergens cause itching, redness, and sometimes blistering. With chronic exposure to an allergen the skin becomes thick, red, scaly, and may later darken and crack. A patch test may be performed to identify the allergen. Once identified, the allergen that causes the reaction should be avoided. Common allergens include rubber (especially latex), nickel, chromates, dyes (in clothing and hair dyes), fragrances, preservatives, medications, poison ivy, and related plants. Mild allergic contact rashes usually respond to topical steroid creams and/or oral antihistamines. Severe rashes may be treated with antibiotics, corticosteroids, or other anti-inflammatory and immunologic agents.