Chan Tui (Cicada Slough): Dispelling Wind and Scattering Heat, Promoting Rash Eruption and Soothing the Throat, Dispelling Nebula and Improving Vision, Extinguishing Wind and Stopping Spasms

Chan Tui (cicada slough) is the molted exoskeleton left after eclosion by cicadas of the family Cicadidae—Crytotympana atrata, Meimuna mongolica, Leptopsalta sp., and related species, commonly known in Chinese as "zhiliao." It mainly contains chitin and protein. It is generally collected in summer and autumn from the ground near trees where cicadas perch; after collection, the soil and impurities are removed and it is dried in the sun for medicinal use.

Chan Tui is a commonly used Chinese medicinal herb and was already recorded in the Shennong Bencao Jing (Divine Farmer's Classic of Materia Medica). Traditional Chinese medicine considers Chan Tui sweet and salty in taste and cool in nature, entering the Lung and Liver meridians. It has the actions of dispelling wind and scattering heat, promoting rash eruption and soothing the throat, dispelling nebula and improving vision, and extinguishing wind and stopping spasms. Modern pharmacology shows that Chan Tui has anticonvulsant, sedative, analgesic, antipyretic, anti-allergic, immunosuppressive, and antitumor effects. Its analgesic action is quite pronounced: apart from the head and feet, which are weakly analgesic, both the whole slough and the body portion have clear analgesic effects. The aqueous extract of Chan Tui shows high antitumor activity against Ehrlich ascites carcinoma cells.

In the Warm Disease (Wenbing) school of TCM there is a classical famous formula called Shengjiang San (Ascending-Descending Powder), composed of Chan Tui, Jiang Can (Stiff Silkworm), Pian Jianghuang (curcuma), and Dahuang (Rhubarb). This is also the antitumor formula most frequently used by Wenbing-school physicians. In the writings of the renowned Warm Disease expert Zhao Shaoqin, almost every prescription he used to treat cancer contained Shengjiang San. The analgesic and antipyretic actions of Chan Tui can also relieve cancer pain and cancer fever in oncology patients.

In modern TCM materia medica textbooks, Chan Tui is classified as a surface-releasing (jiebiao) herb, mainly used for external wind-heat patterns with cough, sore throat, and hoarseness. TCM holds that Chan Tui, being light and cool in nature, belongs to the upper-jiao category of herbs; it enters the Lung meridian to scatter wind-heat and diffuse lung qi and soothe the throat. It is therefore often combined with Bohe (Peppermint), Qianhu (Peucedanum), and Niubangzi (Burdock Fruit) to treat fever and cough at the onset of warm diseases. Chan Tui may also be used with Bohe, Jiegeng (Platycodon), and Gancao (Licorice) to treat lung-qi failing to diffuse due to wind-heat, with hoarseness and sore, swollen throat.

Chan Tui has the effect of promoting rash eruption, so it can be used to treat wind rash with itching or measles that fails to surface—conditions that all cause skin itching. Chan Tui is an important herb for chronic urticaria. There are reports that using Chan Tui alone, or Chan Tui combined with Cili (Tribulus) in a 2:1 ratio, ground into powder and made into pills with refined honey, taken 9 g each time 2–3 times daily with warm water, can effectively cure chronic urticaria or improve clinical symptoms. Chan Tui's rash-promoting action is related to its anti-allergic and immunosuppressive effects.

Chan Tui is also a commonly used ophthalmic herb. TCM holds that it dispels nebula and improves vision; in modern practice, Chan Tui injection is also used to treat corneal nebula. Subconjunctival injection of Chan Tui injection for corneal thin nebula, macula, and leukoderma has a total effective rate of up to 76%.

Traditional TCM uses Chan Tui for red eyes and nebula obstructions, mainly by decoction taken orally. For wind-heat red eyes with excessive tearing, it is often combined with Juhua (Chrysanthemum) and Sangye (Mulberry Leaf); for wind-heat attacking the eyes with nebula film obscuring the vision, it is combined with Gujingcao (Eriocaulon), Mimenghua (Buddleja Flower), and Muzei (Equisetum). In the famous ophthalmic work Yanke Longmu Lun there is a formula called Wu Tui San (Five Sloughs Powder), made from Long Tui (snake slough), Chan Tui (cicada slough), Fenghuang Tui (eggshell membrane), Ren Tui (human fingernails), and Can Tui (silkworm slough), each in equal amounts, burned to ash while preserving nature, and taken as a powder to treat cataract.

Chan Tui also extinguishes wind and stops spasms—described in modern pharmacological terms as anticonvulsant, sedative, and analgesic. In the past it was commonly combined with Bohe, Gouteng (Uncaria), and Zhusha (Cinnabar) to treat pediatric convulsions; it was also combined with Jiang Can, Quanxie (Scorpion), Tianma (Gastrodia), Tiannanxing (Arisaema), and Baifuzi (Typhonium) to treat tetanus. If in an emergency the full formula could not be assembled, Chan Tui alone also had a good wind-extinguishing, antispasmodic effect. Chan Tui is a common pediatric herb; pediatric convulsive epilepsy and persistent high fever can both be treated by grinding Chan Tui into powder for administration.

Chan Tui can also be used for ding abscesses and toxic swellings. The Bencao Gangmu (Compendium of Materia Medica) records that Chan Tui treats "tetanus and ding-type toxic swellings and sores, loss of voice in adults, pediatric lockjaw (jin-feng) and opisthotonus (tian-diao), and genital swelling." The "genital swelling" here refers to edema of the scrotum, mostly caused by allergy; whether the allergy results from weather or insect bites, as long as allergy has caused scrotal edema, it can be washed with a hot decoction of Chan Tui. Ding-type toxic swellings refers to furuncles and carbuncles. The "Chan Tui San" in the Shenghui Fang uses equal parts of Chan Tui and Baijiangcan (Stiff Silkworm), ground to powder, mixed with vinegar, and applied around the ding to reduce swelling and disperse the sore. In the past Chan Tui was also used for pox sores (i.e., smallpox), suggesting it may have anti-smallpox-virus activity; but since the smallpox virus has now been eradicated by humanity, this can no longer be confirmed or refuted.

Chan Tui can also treat rectal prolapse. Roast Chan Tui dry and grind it to powder, mix it with rapeseed oil or Vaseline, apply it around the anus, then gently push the prolapsed rectum back in. During treatment, avoid spicy and irritating foods and keep the stools regular; this can effectively treat rectal prolapse in both children and adults.