[Eczema and food allergy--is there a causal relationship?]

In spite of popular beliefs, the relationship between eczema and food allergy still puzzles researchers and clinicians, which in part is due to the variety of mechanisms involved in various types of allergy. One has to realize the differences between hypersensitivity reactions to food proteins (allergens capable of initiating immediate hypersensitivity or immune complex reactions) and low-molecular weight compounds (haptens that may initiate cytotoxic reactions or delayed-type allergy). Hardly doubted is the role of IgE specific to food proteins in anaphylactic reactions and allergic urticaria. The involvement of food protein-specific IgE also is well-documented in protein contact dermatitis, with exposure to offending allergens occurring mainly through direct contact to the skin. In case of oral intake, protein allergens can provoke oral allergy syndrome or allergic reactions of esophageal mucosa, yet after arriving in the stomach they undergo hydrolytic digestion and loose antigenicity. The popular notion "food allergy causes eczema" was challenged by last decade's research suggesting that allergy to food proteins develops secondarily to eczema, and in the later course manifests as anaphylaxis or urticaria, not eczema. On the other hand, somewhat unnoticed remains the wide array of haptens present in food - be it natural components, food additives (dyes, aromas, preservatives, emulsifiers, etc.) or contaminations (e.g. pesticides, veterinary drugs). Haptens can be absorbed already through oral mucosa, they don't undergo digestion and are capable of provoking delayed-type hypersensitivity reactions strongly resembling atopic eczema. Induction of such reactions can be facilitated by cosmetics that frequently contain the same haptens as food.