Phlegm is a pathological phenomenon that the pathological secretions in the respiratory tract are discharged out of the mouth by coughing. Normal bronchial mucosal glands and goblet cells only secrete a small amount of mucus to keep the respiratory mucosa moist. When various causes in pharynx, larynx, bronchus or lung cause congestion, edema, increased capillary permeability and increased gland secretion of mucosa or alveoli, exudates mix with mucus, serous fluid, inhaled dust and some tissue destruction products, as well as body immune reaction products into sputum. Long term sputum is mostly caused by chronic infectious diseases, such as bronchiectasis, lung abscess, chronic empyema with bronchial fistula, etc. It is suggested that further examination should be carried out to determine the cause of disease and effective treatment should be carried out.
