“Food hypersensitivity” is one type of adverse reaction involving the immune system. The incidence varies due to genetic differences among population groups, diagnostic criteria, and feeding habits. Antigens involved in allergic reaction are called alleregens. Intestinal manifestations of food allergy are the predominant symptoms of food allergy but food can also induce extra - intestinal manifestations as systemic reactions. The diagnosis of adverse food reactions begins with medical history and physical examination. Laboratory test may be useful. Pharmacological treatment for patients with food allergies is indicated when symptoms continue despite best efforts to maintain on allergen free diet. Medications include antihistaminics, corticosteriods, oral cronialyn, prostaglandins synthetase inhibitors, and ketotifen. Oral immunologyical tolerance may be described. The prevention includes allergen avoidance during infancy and detection of cord Blood IgE level.