Indigo naturalis has the functions of clearing heat and detoxification, cooling blood and eliminating spots, purging fire and calming shock. In ancient times, it was also often used for printing and dyeing cloth, thrush, etc. It is mainly produced in Fujian, Yunnan, Jiangsu and other places. It tastes salty and cold. It has the effects of clearing heat and detoxification, cooling blood and eliminating spots, purging fire and calming shock. It is mainly used for febrile disease, rash, hematemesis, hemoptysis, sore throat, mouth sore, children's eclampsia, sore swelling, erysipelas, snake and insect bites, etc.