Many parents ask why their children often get colds. To answer this question, let’s first get to know our immune system. The immune system is like a well-trained elite force that is always defending the health of the body. In general, this force has three functions: first, to defend against infections, second, to remove foreign bodies, maintain stability and prevent the occurrence of autoimmune diseases, and third, to prevent the occurrence of tumors through immune surveillance. Frequent infections indicate a decrease in the defensive function of the immune system, leading to pathogenic bacteria taking advantage of the situation, which leads to the development of the organism. Recurrent pediatric infections are closely related to pediatric immune function. Infants and young children have an underdeveloped immune system and can have physiologically low immune function and are prone to infections, but if others just get a cold and your child gets pneumonia, and other children get better quickly after treatment, but your child does not recover for a long time, then you should be alert to the presence of congenital immunodeficiency disease in your child. The Jeffrey Modell Foundation in the United States has suggested warning signs of congenital immunodeficiency disorders. One is the child’s medical history, 8 or more otitis media in a year, or 2 or more severe sinus infections, or 2 or more pneumonias, or 2 or more deep infections at uncommon sites, or repeated deep skin or organ infections, or infections that require intravenous antibiotics to clear, or infections by uncommon or conditionally pathogenic bacteria, or children with a family history of congenital immunodeficiency disease; the second is the child’s symptoms, children with growth arrest, lack of lymph nodes and tonsils, skin lesions such as dilated capillaries, bleeding spots, etc., fungal skin infections, lupus erythematosus-like rashes, ataxia (which is the easiest sign for parents to detect, such as uncoordinated walking and unstable writing), and thrush and mouth ulcers after one year of age. In both cases, there is a suspicion of congenital immunodeficiency disorder. Congenital immunodeficiency disease, also known as primary immunodeficiency disease, is a condition in which there are defects in immunoreactive cells such as T cells, B cells and macrophages, and/or complement and cellular immunoreactive molecules, resulting in an impaired immune response that makes the body susceptible to infectious diseases, which are usually severe and long-lasting. In addition to being prone to recurrent and severe infections, children with primary immunodeficiency diseases are often associated with abnormalities in self-stabilization and immune surveillance, making them susceptible to autoimmune diseases, allergic diseases, and malignancies. More than 150 primary immunodeficiency diseases have been identified, divided into 8 major categories, including combined T- and B-cell immunodeficiency diseases, antibody-deficient primary immunodeficiency diseases, immunodeficiency syndromes, immune dysregulation diseases, congenital defects in phagocyte number and function, natural immunodeficiency diseases, auto-inflammatory diseases, and complement deficiencies. With advances in medicine, many congenital immunodeficiency disorders can be diagnosed quickly. Once parents suspect that their child has a congenital immunodeficiency disease, they should promptly bring their child to a hospital immunology specialist for consultation. Early detection and treatment are crucial to the prognosis of children with congenital immunodeficiency disorders. If not diagnosed and treated in a timely manner, in mild cases, the growth and development of the child can be affected, reducing the quality of life of the child; in severe cases, the child is likely to die early due to severe infections. The doctor may choose to test several immunological indicators, such as serum immunoglobulin levels, serum IgG subclass levels, serum complement levels, T-cell subsets, B-cell counts, NK-cell counts, phagocyte function, cell surface molecules, and chest radiographs to check for thymus. Cytokines can be tested if necessary, and even genetic testing can be taken to clarify the genetic localization of the disease. Once the diagnosis is confirmed, treatment can be started accordingly, and parents who know the cause of the disease will patiently cooperate with the doctor to help the child fight the disease.