**1. Introduction**

Chronic urticaria can be subclassified into chronic spontaneous urticaria and chronic inducible urticaria. Up to 30% of cases are associated with functional immunoglobulin G antibodies to the high affinity immunoglobulin E receptor FcεRIα or to immunoglobulin A. Pathogenic activation of mast cells and basophils gives rise to release of pro-inflammatory mediators that lead to development of hives. CSU is a debilitating disease with a relapsing course. It affects 0.5–1% of the population at any given time. The duration of CSU is generally 1–5 years but can be longer in cases associated with angioedema and autoreactivity. CSU has detrimental effects on life quality with sleep-deprivation and psychiatric disorders being the most frequent. In a great number of patients an underlying cause or eliciting factor cannot be identified. Among the patients in which an aetiology is suspected, infections, medication, food and psychological factors are most commonly associated. A potential autoimmune cause has been reported in up to 50% of patients. Chronic inducible urticaria is characterised by its ability to be triggered consistently and reproducibly in response to a specific stimulus (pressure, temperature, vibration, water, heat, light). Antihistamines form the mainstay of therapy. In recalcitrant chronic urticaria a variety of other drugs have been tried that include leukotriene receptor inhibitors, conventional immunosuppressive systemic therapy, antiinflammatory and biologic therapy. In this chapter we give an overview of CU and CSU in particular and discuss its diagnosis and management.
