What are causes of chronic urticaria?

• Chronic urticaria (CU) affects 0.5–1% of the general population worldwide with CSU accounting for more than two-thirds of CU cases • Autoimmune disease and may be associated with other autoimmune conditions such as thyroid disease and coeliac disease Circulating 'anti-idiotypic’ antibodies can be detected in 10% of patients with chronic urticaria. These activate IgE bound on mast cells to cause excessive release of chemicals • In most cases, chronic urticaria clears up, but 15% still have papules at least twice weekly after 2 years