The inability to cough up phlegm in the lungs is commonly caused by severe lung infections resulting in thick phlegm that is not easy to cough up; respiratory causes, such as airway obstruction, narrowing, spasm, etc.; or the patient’s own causes, such as weakness or children’s young age. 1. Respiratory infections, such as acute exacerbation of chronic bronchitis, acute bronchitis, pneumonia and so on. When the lungs are infected by bacteria, viruses, fungi, etc., the bronchial tubes are irritated, the exudate increases, and inflammatory substances accumulate to form thick sputum. The more severe the infection, the more secretions there will be. If the phlegm is thicker, it will eventually accumulate in low places and may be harder to cough up. 2. Airway obstruction, narrowing, and spasm can also cause phlegm to be difficult to cough up. When the airway is blocked and narrowed, the exit of sputum is blocked, resulting in the inability to expel sputum smoothly; and when the bronchial spasm occurs, the trachea is weak and the cilia cannot swing normally, which is also unfavorable to the expulsion of sputum. 3. If the patient’s own nutritional status is poor, the inability to cough up sputum or the child’s age is small, will not cough up sputum, can also appear sputum can not be coughed up. If you can’t cough up sputum in the lungs, you should go to the hospital for further examination in order to clarify the cause of the disease and timely treatment.