The clinical definition of small airways is airways with an internal diameter of less than 2mm, and small airway and alveolar inflammation is inflammation that occurs in airways and alveoli with a diameter of less than 2mm. Airways with an internal diameter of less than 2mm are called small airways, which have low airflow resistance and are prone to obstruction. Inflammation of small airways and alveoli commonly occurs in chronic obstructive pulmonary disease, eosinophilic pneumonia and bronchial asthma. Due to recurrent episodes of chronic small airway inflammation, airway narrowing, airway deformation and emphysema can occur. Patients with small airway and alveolar inflammation should seek prompt medical attention to clarify the cause and take targeted treatment to prevent airway structural changes caused by repeated episodes of prolonged airway inflammation.