Alum is a refined product of alum stone and a common Chinese medicine. Chemically speaking, its composition is mainly potassium aluminum sulfate dodecahydrate. In Chinese medicine, alum is considered to have detoxifying, insecticidal, dampness-drying and itch-relieving properties. In ordinary life alum can be used as a water purifier and as an additive in the production of doughnuts, vermicelli and rice noodles. However, because alum contains aluminum, this metal will affect the absorption of iron and calcium after consumption, leading to osteoporosis and anemia, and may also affect the development of nerve cells, so it should be taken internally as little as possible. In terms of dermatology is mainly used externally, external use of alum can play an astringent, antiperspirant, antiseptic, anti-inflammatory effect, with dilute alum solution soak hands and feet, can play the role of antiperspirant, wet application of external rubbing armpit can treat armpit odor.