Research suggests that in some cases, tolerance may be built up by a gradual exposure to an allergenic food. However, the only way of successfully managing a food allergy or intolerance is to eliminate the offending food or food ingredient from the diet, but this should only be done in consultation with suitably qualified experts. Food hypersensitivity includes a wide spectrum of symptoms and mechanisms. Many researchers and clinicians have discussed the possible role of the gut (barrier) and the mucosal immune system in the development of food allergies. Factors that have been addressed in particular include weaning and the weaning diet. Dealing with adults and children with food allergies requires the healthcare professional to have an understanding of the immune mechanisms involved in the development of allergy versus tolerance, diagnostic methods, managing the patient, and the development of new treatment modalities.