Pathophysiology and Symptoms of Food Allergy and Anaphylaxis

Food allergies are increasing in prevalence, have a highly variable clinical presentation, and can result in life-threatening reactions. In order for clinicians to accurately diagnose and manage food allergies, they must have a clear understanding of the symptoms and underlying pathophysiology. Food allergies by definition are immune-mediated responses that occur reproducibly on food ingestion, which differentiates them from non-immunologic adverse food reactions like lactose intolerance or food poisoning. Food allergies can be IgE mediated, non-IgE/cell mediated, or mixed IgE and non-IgE mediated with varying clinical presentations depending on the underlying immune mechanisms. IgE-mediated food allergies produce symptoms that affect the cutaneous (hives, pruritus, angioedema), gastrointestinal (abdominal pain, vomiting, diarrhea), respiratory (rhinorrhea, dyspnea, wheezing), and cardiovascular (hypotension, syncope) systems. IgE-mediated food allergies can progress to anaphylaxis, which is a severe and potentially fatal systemic reaction that requires timely recognition and treatment. Non-IgE- or cell-mediated reactions are typically delayed or chronic, and include food protein-induced allergic proctocolitis (FPIAP), food protein-induced enterocolitis syndrome (FPIES), celiac disease, and food-induced pulmonary hemosiderosis (Heiner syndrome). Mixed IgE- and non-IgE-mediated reactions occur in eosinophilic esophagitis or eosinophilic gastroenteritis, which present with symptoms of dysphagia, vomiting, reflux, and abdominal pain related to eosinophilic infiltrates in the GI tract. This chapter describes the clinical manifestations of food allergies with an emphasis on anaphylaxis and the pathophysiology behind these reactions.