There are many types of urticaria and the principal form of assessment is by clinical history and examination. Urticarial weal formation involves acute, reversible vasodilatation and increased vascular permeability. If the process is deeper the more diffuse swelling is termed angio-oedema. The major types of urticaria include allergic, physical and idiopathic forms. In allergic urticaria, IgE-mediated degranulation of mast cells results in weals of short duration which typically respond well to antihistamines. Physical urticarias are induced by physical insults including pressure, scratch, cold, etc. The distribution and duration of individual weals may suggest the causal factor. Chronic idiopathic urticaria can be very variable, with individual weals lasting between 90 min and 24 hours. Longer-lasting weals are less responsive to anti-histamines and clearly involve other mediators. When long-lasting weals fade leaving a bruised appearance urticarial vasculitis is present which may only respond to systemic corticosteroids. In a proportion of individuals with chronic idiopathic urticaria, auto-antibodies are present with specificity for the high affinity receptor for IgE or sometimes, for IgE itself. In general laboratory tests for allergic factors or other assessments of general health are completely unhelpful.
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