Iron deficiency anemia refers to the anemia that occurs when the body's stored iron is depleted and can no longer meet the needs for normal red blood cell production. Before the production of red blood cells is limited, the body's iron stores are exhausted, but at this time, there are no obvious changes of anemia in the routine blood test; this condition is called iron deficiency. Iron deficiency anemia has its characteristics. Its main clinical manifestations are tissue and organ hypoxia caused by ischemia. Severe iron deficiency anemia can lead to mucosal tissue changes and some nutritional disorders, such as stomatitis, glossitis, atrophic gastritis, lack of gastric acid, dry skin, brittle hair, hair loss, and flat nails, among other changes. Therefore, any factors that cause iron deficiency in the body and affect iron absorption, including increased physiological iron demands, iron storage, and issues in iron excretion processes, can lead to iron deficiency anemia. The main causes can be divided into three aspects:1. Nutritional factors: Individuals such as infants, adolescents, menstruating women, pregnant women, and breastfeeding women are prone to nutritional iron deficiency anemia when the body's iron demand increases.2. Chronic blood loss: This includes gastrointestinal bleeding, heavy menstrual bleeding in women, bleeding hemorrhoids in men, and chronic bleeding from gastrointestinal ulcers, all of which can cause iron deficiency anemia.3. Absorption disorders: Conditions like total or partial gastrectomy can lead to iron deficiency years after the surgery, resulting in iron deficiency anemia.