Although it affects some 30% of children in industrialised countries, the aetiology of atopic dermatitis remains obscure.^1,2 Because up to one third of children with atopic dermatitis have food allergies, foods are frequently invoked as the underlying cause.³ Many families in my practice focus on foods with such intensity that the actual treatment of the skin is marginalised and the patients are miserable (fig 1). Indeed, in one recent study parents had manipulated the diet in 75% of children with atopic dermatitis in attempts to manage their disease.⁴

IS ATOPIC DERMATITIS AN ATOPIC DISEASE?

Atopy is an environmentally influenced syndrome in which the primary immunological abnormality is the production of allergen-specific immunoglobulin E (IgE).^5,6 The clinical image of massive facial oedema, urticaria, and pruritus minutes after eating a peanut in an individual with significant levels of IgE to peanut beautifully illustrates this definition. Entering the home of a cat-owner and, within minutes, sniffling, sneezing and wheezing also nicely paints the picture of an individual who is specifically sensitive to a cat antigen. But atopic dermatitis seems to defy this model with its non-immunological characteristics such as impaired skin barrier function, an often unpredictable course of waxing and waning, and up to two thirds of patients without any measurable allergen-specific IgE antibody.^7–9

Indeed, the fact that atopic dermatitis is seen in patients with X linked agammaglobulinaemia—a state in which there is almost no IgE at all—seems to cement the notion that atopic dermatitis is not IgE-related, and thus not an atopic disease.¹⁰ …