Hemoglobin is hemoglobin. There are many reasons for low hemoglobin, including anemia, malignant blood system diseases, and long-term use of chemotherapy drugs. 1. Anemia: long-term malnutrition, postpartum, post-surgery, peptic ulcer, trauma and other reasons may cause lower hemoglobin. Among them, long-term malnutrition is mainly caused by the lack of raw materials for blood production, and postpartum, post-surgery, peptic ulcer, trauma, etc. are mainly caused by excessive blood loss, which leads to anemia, thus causing low hemoglobin. Other diseases that can cause anemia include aplastic anemia, severe liver disease, hemolytic anemia, systemic lupus erythematosus and so on. 2. Malignant hematologic diseases, such as leukemia and myelodysplastic syndromes, can cause abnormal bone marrow proliferation, reduce the production of normal bone marrow hematopoietic cells, and inhibit the production of red blood cells, which will lead to low hemoglobin. 3. Long-term use of chemotherapeutic drugs: such as cytarabine, vinblastine, hydroxyurea, etc., can also lead to bone marrow suppression, reducing the production of red blood cells, thus causing a decrease in hemoglobin. If hemoglobin is lowered, it is recommended to consult a doctor in a timely manner to clarify the cause of the disease and carry out targeted treatment with the help of the doctor.