Immunologically mediated hypersensitivity to foods is defined as food allergy, mainly due to immunglobulins of class E (IgE) triggering immediate reactions (type I hypersensitivity) with possible involvement of mucosa, skin, airways, intestinal tract, and the vascular system. Primary food allergy is based on (early) IgE sensitization against animal (e. g., cow's milk, hen's eggs) or plant proteins (e. g. peanut, hazelnut or wheat). In the case of secondary food allergies, IgE against pollen proteins (e. g., birch) reacts to structurally related food proteins (with cross-reactions to stone and pit fruits). Non-immunological food intolerance reactions are mostly based on carbohydrate malassimilation (e. g., lactose intolerance, fructose malabsorption) and are rarely due to pseudo-allergies (e. g., flavors, dyes, preservatives) primarily in patients with chronic urticaria. Common intestinal symptoms are mainly due to functional disorders (e. g., irritable bowel disease), rarely because of inflammatory intestinal diseases (e. g., celiac disease). Histamine intolerance, gluten hypersensitivity, and so-called food type III hypersensitivities are controversial diagnoses. The aforementioned disease entities/models are of variable importance for the affected individuals, the public health system, and society in general.
Keywords: Adverse reaction; Allergen; Food allergy; IgE; Intolerance.