Inability to cough up sputum is mainly due to the fact that sputum contains very little water, the airways are very dry, the state of airway congestion and edema is more pronounced, and there is little inflammatory secretion. It is commonly seen in dry bronchiectasis, but also in chronic wheezy bronchitis, cough-variant asthma, and idiopathic diffuse interstitial fibrosis. Mainly due to these diseases, the airway mucosa appears to be significantly congested, and after being stimulated by inflammation, the mucosal wall becomes congested and edematous to varying degrees, and coughing symptoms appear. It is also seen in occupational lesions of the airway, such as bronchopulmonary carcinoma in the early stage, the cancer will compress the airway, but there is no airway secretion, resulting in the symptom of coughing but not coughing up sputum.