Cough with coughing of grayish-yellow sputum is usually caused by a bacterial infection of the respiratory tract. It is more common in infectious diseases of the lower respiratory tract, such as pneumonia, bronchiectasis, lung abscess and so on. 1. Pneumonia: its common symptom is coughing up sputum, when the infection is further aggravated, purulent sputum or bloody sputum may appear, due to the infection of the bronchial mucous glands mucus secretion increases, the permeability of the capillary wall increases, the plasma exudates, the exudate and the mucus, the inhalation of dust and some tissue destruction mixed with grayish-yellow sputum. 2. Bronchiectasis: the main symptom is recurrent or persistent coughing up sputum or coughing up yellowish sputum, the occurrence of yellowish sputum is usually combined with bacterial infections, and with the aggravation of the infections, yellowish sputum will increase. 3. Lung abscess: coughing up pus-filled sputum, caused by liquefaction of necrotic tissue from the abscess breaking down into the airways, which can be accompanied by fever and chills. Therefore, when coughing up grayish-yellow sputum repeatedly, it is necessary to combine with other symptoms and relevant examinations to further clarify the cause of the disease and timely treatment.