Fumaric acid, also known as fumaric acid, corylic acid, or lichenic acid, is a colorless, flammable crystal derived from butylene, known as fumaric acid (IUPAC name: (E) - butyric acid). Its chemical formula is C4H4O4. Burning fumaric acid will release irritating maleic anhydride smoke. It is one of the participating substances in the citric acid cycle, with a fruity aroma, and can be found in the genus Corydalis, Boletus, lichens, and Icelandic seaweed.
Fumaric acid can be used to manufacture polyester resins and polyols, as well as as as a mordant or seasoning for dyes. It is a common food additive and dietary supplement, and sometimes used as a substitute for tartaric acid in beverages or fermented powders.
biology
Cells use fumaric acid to generate energy from food. Human skin also naturally produces fumaric acid under sunlight.
pharmacological action 
Due to the fact that the cause of psoriasis is a deficiency in the production of fumaric acid in the skin, fumaric acid is sometimes used as a treatment for this condition. At the beginning, the dosage was 60-105mg per day, but gradually increased to 1290mg per day thereafter. The side effects of using fumaric acid include kidney or digestive system diseases, as well as skin and redness, which are caused by excessive use. After long-term use, there may be a decrease in white blood cells.
food
Since 1946, fumaric acid has been used as a food acidifier due to its non-toxic properties. It is widely used in beverages and fermented powders with a focus on purity, such as Willow's grape juice. It is generally used as a substitute for tartaric acid, or sometimes as a substitute for citric acid. To maintain the same taste as citric acid, the ratio of fumaric acid to citric acid is 0.91g to 1.36g.