[Atopic dermatitis in children and food allergy: combination or causality? Should avoidance diets be initiated?].

Atopic dermatitis (AD) is one of the first manifestations of the atopic march. The natural history of food allergies (FA) is closely related to AD. Sensitivity to food is demonstrated with cutaneous tests (prick-tests and atopy patch-tests) or the presence of IgE specific to food. A true allergy to a foodstuff is revealed by oral provocation tests (OPT) or by improvement during an avoidance diet. Ingestion of the food allergen during OPT can provoke an onset of eczema, an immediate reaction (urticaria, oedema) or involve other target organs (digestive disorders, rhinitis, asthma or anaphylactic shock). Seven allergens are responsible for around 90 p. 100 of FA: milk, eggs, wheat, peanuts, nuts, soy and fish. The fundamental knowledge acquired demonstrates the implication of food allergens in the physiopathogenesis of AD. The assessment of the efficacy of avoidance diets is difficult to demonstrate in standardised double-blind studies. Their efficacy is demonstrated compared with the natural history of AD. A diagnostic algorythm of FA during AD is proposed. An avoidance diet can be prescribed on 3 levels: primary, secondary and tertiary prevention. Diagnostic dietetics are aimed at initiating a hypoallergenic diet over a short period of 15 to 21 days when AD is severe and does not permit an allergy assessment. This diet is followed by an allergy assessment and OPT to determine the foodstuff responsible. Therapeutic dietetics consists in initiating an avoidance diet based on the results of the allergy assessment: positive predictive value of specific IgE, positivity of oral provocation tests or the re-introduction of the foodstuff for one week. Preventive dietetics is aimed at preventing the onset of AD: a consensus has been established by the American and European Academies of Paediatrics. In conclusion, present knowledge demonstrates that FA is a triggering factor for AD and that the avoidance diets based on allergy assessments are an essential tool in the treatment of AD. Understanding the triggering mechanisms of oral tolerance will permit the development of strategies for the prevention and cure of food allergies.