White sputum may be caused by respiratory tract infections, long-term smoking, allergies and other reasons. 1. Respiratory tract infections: often due to pathogenic infections, resulting in inflammation of the respiratory tract, such as acute bronchitis, acute bronchitis, pneumonia, airway mucosal secretion increases will produce white foamy sputum or mucus sputum. 2. Long-term smoking: long-term smoking is easy to cause chronic inflammation of the respiratory tract, due to long-term stimulation of nicotine and other ingredients in cigarettes, which will cause excessive secretion of mast cells and cause white sputum. 3. Allergy: allergic respiratory inflammation caused by a variety of allergens, stimulation of the respiratory mucosa will also appear white phlegm, such as allergic bronchitis, eosinophilic bronchitis or bronchial asthma. When coughing up white phlegm, it is recommended to consult a doctor for further examination, to clarify the cause with the help of the doctor, and to carry out targeted treatment or therapy.