Is coughing with white phlegm a sign of cold lung or hot lung?

Coughing with white phlegm, in traditional Chinese medicine (TCM) theory, is typically considered a manifestation of cold in the lung. This is primarily because white phlegm tends to be thin in texture and clear in appearance, which is associated with cold affecting the lung and insufficient yang energy. Cough due to cold in the lung is often caused by the invasion of external cold and wind-cold pathogens, leading to impaired lung function and symptoms such as cough, sore throat, chills, fever, clear nasal discharge, or excessive white phlegm accompanied by coughing. Although coughing with white phlegm is commonly related to lung cold, white phlegm may also appear in certain situations such as the early stage of lung heat or other pulmonary diseases. Therefore, it is not sufficient to diagnose lung cold or lung heat based solely on the symptom of coughing with white phlegm; a comprehensive assessment integrating the patient's overall symptoms is necessary. If coughing with white phlegm persists, prompt medical consultation is recommended.