Adverse reactions to food which occur only in susceptible individuals may result from true physical hypersensitivity to components of foods or from psychological factors. Non-allergic food hypersensitivity may be due to a metabolic defect in the affected individual, while in food allergy immune mechanism is involved. Food allergy can be further subdivided into IgE-mediated food allergy and non-IgE-mediated food allergy, depending on the underlying allergic mechanism. Most cases of confirmed food allergy involve the production of IgE antibodies and a network of interactions between various cell types and chemical mediators. This type of allergic reaction is known as an IgE-mediated allergy (or a type I hypersensitivity reaction), and it produces immediate symptoms. The most severe form of IgE-mediated allergy is systematic answer known as anaphylaxis that can be fatal in the absence of adequate medical help. Other less severe allergy manifestations are symptoms like swelling, itching, redness and heat in the mouth, gut, skin or respiratory tract. Hypersensitivity to food requires special dietary treatment, but total exclusion of some foods from the diet can be very difficult, because of the wide distribution of some foodstuffs in the diet or their presence as impurities in other foods. It is very important that producers have good systems of control, traceability and labeling of possible presence of food allergens in order to help people with food allergies to conduct their restrictive diets that are in most cases their lifelong treatment.