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.

This disease can also be caused by malnutrition of the skin due to insufficiency of the liver and kidney, dysfunction of the thoroughfare vessel and conception vessel, and deficiency in the Ying-Nutrient System and Xue-Blood System in females. If prolonged accumulation of blood heat is attacked by pathogenic damp toxin simultaneously, it can cause complication of heat toxin mixed with dampness. If the meridians and collaterals are obstructed by exogenous wind, dampness and heat toxin, it can lead to joint affection. If heat toxin is not relieved to induce excessive fire toxin and flaring-up of qi and blood, it can cause severe affection of red skin and desquamation in the whole body