Pneumonia in a child once a month may be related to the imperfect development of the body function, vitamin deficiency, and the existence of underlying diseases, etc., and needs to be analyzed on a case-by-case basis. 1. Imperfect development of body functions: for younger children, the immune function and respiratory tract are imperfectly developed, and pathogens can easily attack the body and cause frequent respiratory infections. 2. Vitamin and trace element deficiencies: most common in children with unbalanced diets or malnutrition, which can affect their immune function and growth and development, resulting in the above conditions. 3. Underlying medical conditions: primary immunodeficiency diseases, pulmonary cysts, pulmonary vascular developmental abnormalities or tetralogy of Fallot can affect cardiopulmonary function, leading to recurrent respiratory infections, as described above. 4. Others: air pollution, passive smoking environment, adenoid hypertrophy, etc. can lead to respiratory tract infections, and some children may develop pneumonia once a month. It is recommended to consult a specialist to evaluate and determine the cause of the disease.