Red flags The following findings are of particular concern: Angioedema (swelling of the face, lips, or tongue) Stridor, wheezing, or other respiratory distress Hyperpigmented lesions, ulcers, or urticaria that persist > 48 hours Signs of systemic illness (eg, fever, lymphadenopathy, jaundice, cachexia) Interpretation of findings Acute urticaria is nearly always due to some defined exposure to a drug or physical stimulus or an acute infectious illness.