Atopic eczema is one of the most common skin diseases of our time, and has commonly been regarded, without further proof, as caused by allergic factors. Although allergy may be involved in some cases, it is probably no more than an exacerbating factor and not the underlying cause. This has important implications for diagnosis and therapy. In recent years the interest has centred on the functional aspects of the skin barrier, with emphasis on lipid constituents in stratum corneum. The authors present some new data on the barrier function which are relevant to diagnosis and therapy.