Coughing up yellow pus sputum is generally considered to be a bacterial infection of the respiratory tract, such as pneumonia, lung abscess, bronchitis or acute exacerbation of chronic lung disease, rhinitis and sinusitis. 1. In general, mucus is secreted from the nasal cavity to the respiratory tract, which is a kind of protective layer of the organism itself. However, when induced by bacteria, viruses and allergens, the mucus secretion in the airway increases, and coughing up is phlegm. 2. Coughing up yellow sputum is considered to be a bacterial infection, as well as yellow sputum caused by viruses, which are related to the metabolism of bacteria and viruses, causing pneumonia, inflammation of the pharynx, bronchitis, lung abscess and other diseases, and may also be accompanied by fever and general malaise. 3. Yellow sputum may also appear in acute infections of chronic lung diseases, such as bronchial dilatation and infection, acute exacerbation of chronic obstructive pulmonary disease, tuberculosis activity, interstitial fibrosis and infection. 4. Rhinitis, sinusitis: nasal purulent secretions, backflow to the throat, with coughing phlegm coughing out will also be yellow-green sputum. In short, coughing yellow sputum timely medical examination, clear causes, treatment.