Background: The pathogenesis of chronic idiopathic urticaria is characterized by defective histamine release.

In 80% of cases, a cause is not identified and this is classified as chronic idiopathic urticaria.

Chronic idiopathic urticaria (CIU) is characterized by the increased releasability of histamine by mast cells in normal-appearing skin.

Chronic spontaneous urticaria, formerly also known as chronic idiopathic urticaria and chronic urticaria (CU), is more common than previously thought.

The ability of basophils from patients with allergic rhinitis, extrinsic asthma, chronic idiopathic urticaria and atopic dermatitis to release histamine spontaneously in vitro was studied.