Psoriasis is a commonly and frequently encountered chronic inflammatory dermal disease. The duration of this disease is comparatively longer and it occurs mostly in the young adults and is one of the dermal diseases for emphatic study at present. The etiology and pathogenesis of this disease is still unknown and may be related to genetic, infective, and metabolic, endocrine, nervous, mental, and immunological disturbance. In Chinese medicine this disease is called "Bai Pei (Psoriasis)" and "Song Pi Xian (Psoriasis)". It is mostly caused by blood heat, or constitutional blood heat plus invasion of pathogenic wind and heat, or heat produced by exogenous wind and cold, or heat transformed from long stagnation due to emotional injury and stagnation of qi, or heat produced from stagnation due to qi dysfunction and disharmony of the spleen and stomach due to excessive intake of irritating seafood,or excessive heat and wind due to accumulation of pathogenic heat in the Ying-Nutrient System and Xue-Blood System, or damage of yin and blood, leading to blood deficiency and wind dryness due to gradual subsidence of blood heat after a long duration, or obstruction of the meridians and collaterals, leading to qi stagnation and blood stasis.