Anorexia nervosa is a common condition in which children lose their appetite for a longer period of time or even refuse to eat. Anorexia is also one of the common symptoms of many diseases that suggest digestive system dysfunction. The causes of anorexia are mostly due to two pathophysiological factors: one is the effect of local or systemic diseases that lead to disorders of the digestive system, and the other is the effect of the central nervous system, where various stimuli in the internal and external environment of the human body affect the central nervous system, leading to an imbalance in the regulation of digestive functions. The common causes of anorexia in children are: 1. gastrointestinal diseases such as acute and chronic gastritis, peptic ulcer, acute and chronic hepatitis, chronic enteritis, various causes of diarrhea and long-term constipation, gastrointestinal metaplasia and certain drugs that can easily cause gastrointestinal irritation such as erythromycin and sulfonamides; 2. systemic organic diseases such as tuberculosis and other chronic infections, certain endocrine system diseases such as hypothyroidism, adrenocorticotropic hormone deficiency, and other chronic infections, Relative deficiency of adrenocorticotropic hormone may also manifest as anorexia. 3. Zinc or iron deficiency of trace elements; 4. Long-term intake of salt-free diet; 5. Vitamin A and vitamin D poisoning; 6. Bad eating habits: the main cause of anorexia in children. The formation of poor eating habits is related to many factors. Including: unreasonable family management strategies, improper feeding, deviated ingestion behavior, deviated food types, lack of effective countermeasures, lack of basic knowledge of organizing balanced meals for families, etc. 7. High ambient temperature or fever; high temperature or high humidity can affect gastrointestinal function, lower digestive juice secretion, lower digestive enzyme activity and reduced gastric acid, resulting in decreased digestive function and anorexia. 8, too little activity, or sleep too late; 9, anorexia nervosa: only refers to a type of anorexia caused by mental factors. The pathogenic factors and clinical manifestations are as follows: (1) Acute mental stimulation: after the child is strongly frightened, the spirit is depressed, the activity is inhibited, and the appetite is reduced. This kind of anorexia, often not too long, the psychological scare past appetite will be restored. (2) Sub-acute or chronic mental stimulation: When leaving relatives and familiar environment to enter a nursery or other new environment, the child does not adapt to the new environment, is depressed, has a reduced appetite, and sometimes vomits after meals. Family misfortune or parental divorce, etc. (3) Influence of wrong education: Parents demand too much from the child, restrict freedom, prevent playing with other children, or restrict where he wants to go, which affects his mood and makes his appetite decrease. Or parents pay too much attention to children eating, repeatedly induce or use threatening means to cause revulsion and anorexia. (4) Stubborn anorexia nervosa: Individual girls with anorexia nervosa can be very serious, the patient is extremely thin and weak, similar to severe malnutrition. Such as low body temperature, fear of cold, slowed heart rate, low blood pressure, cyanosis of extremities, amenorrhea in older girls, anemia, and features of vitamin and protein deficiency.