A new episode of urticaria and/or angioedema can be an anxiety-inducing event for both the patient and the physician(s) seeing them in primary care, urgent care, or the emergency department. These events are commonly mistaken for "allergic" reactions and often mistreated. The most common causes of new onset urticaria in older children and adults, with or without angioedema, and normal vital signs or hypertension, are post-infection or acute idiopathic urticaria. These patients are not helped by

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... systemic steroids, which may cause morbidity. An IgE-mediated allergy is almost never the cause. These episodes are easy to manage and virtually never life-threatening. Acute idiopathic urticaria is treated with high-dose nonsedating antihistamines acute avoidance of alcohol and nonsteroidal anti-inflammatory drugs, and time. An epinephrine prescription is not indicated for onset acute urticaria or angioedema, unless there is a strong suspicion of anaphylaxis, and they have been acutely treated with epinephrine. When anaphylaxis is suspected, because of hypotension or hypoxia, the treatment of choice is intramuscular epinephrine and supportive care. An acute tryptase then needs to be obtained within 1 to 3 hours of symptom onset, prior to a referral to Allergy. Most angioedema, without itching or hives, is idiopathic. Treatment is supportive care and time. Antihistamines, epinephrine, and systemic corticosteroids are completely ineffective in treating idiopathic or bradykinin-mediated angioedema. Suspect hereditary or acquired angioedema if there is recurrent non-itchy swelling with abdominal pain triggered by mechanical trauma. Only check a C4 prior to a referral to Allergy for a formal diagnosis and long-term management.