Urticaria refers to a localized edematous reaction due to dilation and increased permeability of the small blood vessels of the skin and mucous membrane. Its etiology is complicated and the causative reason is unknown in about 3/4 patients. The commonly encountered causative factors are medications, foodstuffs and additives, inhaled substance (such as pollen, skin scale, fungous spore), infection (bacterial, viral and parasitic infection), insect bites, mechanical, heat and light irritation, emotional factors and endocrine change, genetic factors and systematic diseases, etc.

The pathogenesis of urticaria is divided into two types of immunity and non-immunity. Urticaria related to immunity is mainly caused by type I or type IIIallergic reaction. This disease belongs to the category of "Insidious Rash" in Chinese medicine and its onset is mostly related to exogenous wind that attacks repeatedly to cause blood deficiency and wind dryness.