Urticaria is a common cutaneous disease characterized by recurrent and transient wheals and pruritus, sometimes accompanied angioedema. The classification of urticaria is based on the duration of the disease and whether extrinsic triggers are identified or not. Acute urticaria is usually occurred by specific causes, such as drug, food, and infection, etc. Therefore, acute urticaria can be remitted within 6 weeks just by avoiding the exposure to the causes. However, chronic urticaria defined as

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... epeatedly occurred itchy wheals and/or angioedema for at least 6 weeks, has a significant effect on patients' quality of life. Chronic inducible urticaria can be triggered by various physical stimuli including dermographism, delayed pressure, cold, heat, cholinergic stimuli, sunlight, and exercise. Chronic spontaneous urticaria (CSU) is diagnosed when no specific extrinsic cause is identified in the patients. CSU due to autoimmune mechanism accounts for 30-50%, autologous serum skin test and anti-thyroid autoantibody can be evaluated. However, various physical stimuli, emotional or physical stress, drugs, particularly aspirin and non-steroidal anti-inflammatory drugs can exacerbate urticaria in 30-75% of patients with CSU. Allergic diseases and autoimmune diseases are more common in CSU patients than in general populations. To assess the severity of urticaria and to adjust treatment step, urticaria activity score over 7 days, calculated by the number of wheals and the severity of pruritus, is recommended by recent international guidelines. (Korean J Med 2019;94:353-357)