Atopic dermatitis is a chronic inflammatory skin disease associated with elevated serum IgE levels and sensitization to a variety of inhalant, food and microbial allergens. Controlled challenges have provided substantial evidence that allergens can trigger acute IgE-mediated mast-cell dependent exacerbations of eczema in these patients. However, the sustained chronic skin inflammation that characterizes atopic dermatitis is likely to result from a local expansion of allergen-specific T helper type 2 cells that produce interleukin-4 and interleukin-5 and the concomitant infiltration of eosinophils. An important role for IgE in allergen presentation to T helper type 2 cells by Langerhans cells has been proposed. These observations may have important implications for the development of new approaches for the treatment of this increasingly common allergic disorder.