The severity of anemia is determined by the degree of reduction in hemoglobin concentration. Anemia is caused by impaired red blood cell production, blood loss or excessive red blood cell destruction. Acute anemia can cause severe symptoms or even shock even if the anemia is mild. Chronic anemia, on the other hand, can be asymptomatic or less symptomatic due to the good compensatory function of the organs in the early stage, and only when the compensation is not complete do symptoms gradually appear. The main symptoms are pale skin and mucous membranes, and extramedullary hematopoiesis may appear in infants and children. (1) Respiratory and circulatory system: the organs and tissues may suffer from different degrees of hypoxia, and the baby may experience shortness of breath, rapid heartbeat and other uncomfortable symptoms with a little movement; in severe cases, the child may experience heart enlargement, systolic murmur in the precordial area and heart failure. (2) Digestive system: It can cause a decrease in gastric acid secretion and poor fat absorption, making the baby’s digestive ability weakened. It causes the baby’s appetite to decrease, nausea, abdominal distension, etc. (3) Nervous system: baby’s anemia, oxygen uptake capacity decreases, brain tissue is deprived of oxygen, baby’s memory and attention, etc. will be affected. Mental inactivity, inattention, restlessness or drowsiness, older children may complain of dizziness and tinnitus. (4) Immune system: It can cause defective cellular immune function, resulting in poor resistance of the baby and easy to get sick.