Yellow phlegm in morning brushing is mainly considered to be caused by bronchitis, tonsillitis, upper respiratory tract infection and other respiratory diseases, but the possibility of rhinitis, sinusitis and other inflammatory diseases of the nasal cavity cannot be excluded. The local inflammation of respiratory system diseases causes inflammatory repulsion of the epithelial mucous membrane tissue of the bronchial tubes, causing inflammatory cells such as lymphocytes and eosinophils to gather and engulf pathogenic bacteria, viruses and harmful microorganisms to form sputum, which is pushed to the upper respiratory tract with reflex coughing and movement of the epithelial cilia tissue of the bronchial tubes and then expelled from the body. Yellow phlegm is discharged by coughing when the throat is stimulated during morning brushing. The cause of yellow sputum from inflammatory nasal diseases is mainly due to the secretion of purulent substances caused by local inflammation of the nasal cavity, the opening of the sinuses is lower during sleep, and the drainage of inflammatory secretions in the sinuses is smoother when lying down than when standing upright, and some of the purulent secretions flow to the posterior pharyngeal wall at night, and yellow sputum appears in the morning after waking up.