I. Overview: As a traditional treatment for internal and external diseases, the medicinal bath has a long history. The Book of Rites? Qu Li”: “If there is a sore on the head, take a bath; if there is an ulcer on the body, take a bath.” In the Eastern Han Dynasty, Zhang Zhongjing popularized the bathing method in clinical practice, and the Treatise on Miscellaneous Diseases of Typhoid Fever contained a formula for washing the body with lily to cure lily disease, and a bath with bitter ginseng soup to treat fox disease, etc. Li Shizhen’s “Compendium of Materia Medica” recorded the following about skin disease medicine bath: water pimples for wind-heat itching, decoction bath, get sweat; willow branches and root bark, wash wind swelling. By the Ming and Qing dynasties, the development of medicinal bath method was mature, and the related mechanism was explored, such as Wu Shiji’s “Rei Bo Era” proposed “the theory of external treatment is the theory of internal treatment” and “although the treatment is external, it is no different from the treatment of internal” and other famous assertions. Second, the mechanism of herbal medicine bath (bath): the mechanism of action of the medicine bath is the action of drugs on the whole body muscle surface, local, the affected area, and by absorption, circulating meridians and blood vessels, internal organs, from the surface to the inside, and thus produce effects. The medicinal bath can be used to unblock the meridians, activate blood and silt, dispel wind and cold, clear heat and detoxify, relieve swelling and pain, adjust yin and yang, coordinate the internal organs, pass through the qi and blood, moisten the whole body and other health effects. Modern pharmacology also confirms that a medicinal bath can increase the content of certain immunoglobulins in the blood and enhance the elasticity and vitality of the skin. From the perspective of Chinese medicine, the mechanism of action of herbal bath has the following points, one of which is that herbal baths prevent and treat diseases in a different way than internal treatment. As the Suwen Yin and Yang Ying Xiang Daxue said, “Those who have evil, impregnate the form as sweat.” It shows that the external application can also help Yang to transform Qi and make the evil come out from sweat. Secondly, human is a unified whole, the five organs and six internal organs and the limbs and bones are connected through the meridians. As Wu Shangxian’s “The Encyclopedia of the Rational Boiling” says: “In order to cure the disease, the skin is separated but the hair orifice is open, and the internal organs are not seen, so it is straight to the internal organs”. Thirdly, Chinese herbal medicine therapy uses heat and herbal medicine to produce a large amount of medicinal steam and a large amount of herbal ions after decoction to act on the skin, so that the skin capillaries expand, blood circulation is accelerated, tissue regeneration and cellular vitality are accelerated, histamine-like substances are discharged, and the active ingredients of the medicine penetrate into the couples through the skin and orifices. The active ingredients of the drug penetrate into the couples through the skin and orifices, unblocking the sweat holes, thus achieving the purpose of expelling wind and cold, unblocking stagnation, dispelling wind and relieving itch. From the modern medical research on the physiological role of the skin is to play the premise of the medicinal effect of the bath, modern medicine believes that the skin is the largest organ of the human body, in addition to the role of protection. It also has a variety of functions such as absorption, penetration, sensation, secretion and excretion, and plays an important role in the physiopathology of the human body. Research has proved that drugs are absorbed through the skin and reach the disease; at the same time, a large number of nerve endings and special receptors distributed in the skin can affect the nearby receivers in the stimulation, thus regulating the function of nerves, body fluids and circulation, improving the activities of the corresponding tissues and organs to enhance the body’s resistance to disease and repair ability. In addition, the secretion, excretion and metabolic functions of the skin are involved in the excretion of metabolites such as uric acid, urea and some inorganic salts, as well as the elimination of toxins and accumulated metabolic wastes from the body, which is called “the removal of evil from the body” in Chinese medicine.