RT Book, Section A1 Creswell, Caleb A2 Soutor, Carol A2 Hordinsky, Maria K. SR Print(0) ID 1190937765 T1 Urticaria T2 Clinical Dermatology: Diagnosis and Management of Common Disorders, 2e YR 2022 FD 2022 PB McGraw-Hill Education PP New York, NY SN 9781264257379 LK dermatology.mhmedical.com/content.aspx?aid=1190937765 RD 2024/03/28 AB Urticaria (hives) is defined by the rapid appearance of lesions called wheals, which consist of dermal swelling presenting as pruritic papules or plaques with or without surrounding erythema. Wheals are smooth with no surface changes. Individual wheals last for 1–24 hours. Wheals form when mast cells release histamine in response to various stimuli. Urticaria is divided into acute (duration less than 6 weeks) and chronic (duration greater than 6 weeks) forms. Chronic urticaria can occur spontaneously or as a result of physical stimuli.