Urticaria (hives) and angioedema are very common, affecting more than 20% of people during their lifetime.15 They are classified as acute if lasting less than 6 weeks or chronic if lasting for more than 6 weeks.15 Acute urticaria describes raised and slightly erythematous wheals or papules that are pruritic and edematous (Figs. 67-6 and 67-7). Acute urticaria favors the trunk and extremities and is a transient process with new crops of hives appearing and resolving over several hours. Angioedema results from the same IgE-mediated process as urticaria, but involves deeper dermal and subcutaneous tissues.15 Angioedema favors the face, lips, tongue, mouth, genitalia, and extremities.16 In children, the most common triggering agents for acute urticaria include infections, medications, and foods.15 For younger children, the most common foods that cause urticaria are egg, milk, soy, peanut, and wheat. For older children, common triggering foods are fish, seafood, nuts, and peanuts.15 Viral infections can commonly cause pediatric urticaria.17 Frequently, chronic urticaria is accompanied by angioedema and is most often idiopathic. Less frequently, children may suffer from physical urticaria, which can be brought on by pressure, exercise, contact with water, cold exposure, or less commonly sun exposure.16