The 2-year-old boy, Mingming, looked much thinner than children his age. He had a fever and umbilical cord infection 6 days after birth, followed by recurrent pneumonia, diarrhea, red and swollen gums and mouth ulcers. At first, the family thought it was normal for children to have a weak constitution and low immunity, and that they would get better as they grew up. Two years passed, but Mingming’s recurrent infections showed no signs of improvement, which attracted the parents’ attention. He was taken to a tertiary care hospital in Shanghai, where he was examined in detail and finally diagnosed with immunodeficiency, a form of congenital immune deficiency. In the eyes of the general public, it is often difficult to distinguish the specific meanings of the terms immune deficiency and immunodeficiency, so they are confused, and some delay treatment as a result. It is well known that the immune system of infants and young children is not yet mature, and they often have immune deficiency at this time. The other two conditions are congenital hypoimmunity and acquired secondary hypoimmunity, both of which are pathological and require special treatment. Physiological immunodeficiency is actually a physiological phenomenon in the human body and is not a pathology. Similar to the development of human intelligence, no one would or should expect a child to have the same intelligence as an adult. Similarly, we cannot expect a young child to have the same immunity as an adult. Congenital immunodeficiency, also known as immunodeficiency, is a condition in which one or more components of the immune system lose their original function due to genetic mutations and other factors, and immunodeficiency occurs. Ming Ming is one of these cases. The proportion of children with this type of disease is low, and the disease is usually severe and long-lasting. The main manifestations are: recurrent infectious diseases such as sepsis, pneumonia, otitis media, meningitis, diarrhea, skin infections, etc.; poor treatment of infections and prolonged illness; severe infections after normal vaccinations; similar family history; and susceptibility to malignant diseases such as tumors and leukemia. Common immunodeficiency diseases include antibody deficiency, T-cell deficiency, combined immunodeficiency, defective phagocyte function, and complement deficiency. Acquired secondary immunodeficiency, as the name implies, is immunodeficiency induced by external factors after birth. Immune function can often be restored after removal of the cause of these disorders. Common causes of acquired secondary immunodeficiency include malnutrition, such as protein, calorie, vitamin, and mineral deficiencies; use of immunosuppressive drugs, such as hormones, antineoplastic drugs, or exposure to radiation; HIV infection due to human immunodeficiency virus; and so on. In immunocompromised children, it is first necessary to find out which of the three conditions mentioned above belongs to the child, and sometimes an experienced doctor needs to make a diagnosis with the help of effective tests. In case of congenital immunodeficiency, early diagnosis is very important to improve the prognosis of the child. Several of the more common genetic diagnoses of congenital immunodeficiency have been carried out in China. The treatment of congenital immunodeficiency requires different measures according to the condition, and the general treatment is more difficult and requires more lasting treatment. Although physiological immune deficiency is a normal phenomenon that each person must experience during the process of growth, but mastering the necessary knowledge of home care can help improve the baby’s immunity and reduce the chance of infection. Family care needs to follow the “five good” principle: good mind adjustment, good physical exercise, good sleep and rest, good protection against cold and warmth, and good dietary arrangements. In order to ensure that our little one grows up quickly and thrives.