Urticaria, angio-oedema and anaphylaxis.

laxis are distinct clinical entities caused by transient plasma leakage from small blood vessels. When the affected vessels are superficial the result is a raised, itchy swelling of the skin known as a weal. Involvement of deeper vessels produces tender subcutaneous and submucosal swellings known as angio-oedema. Generalised plasma exudation leading to shock is a feature of anaphylaxis but also occurs in anaphylactoid reactions and the capillary leak syndrome.