Urticaria, angioedema or other urticarial disorders

**Definition:** A heterogeneous group of disorders characterised by dermal and/or subcutaneous and submucosal oedema. The most common underlying mechanism is release of histamine from mast cells with consequent capillary dilatation and tissue oedema. This is responsible for the weals of spontaneous and most physical urticarias. A variety of other mechanisms are involved in other urticarial disorders.

**Exclusions:** - Urticaria pigmentosa - Papular urticaria