In traditional Chinese medicine, coughing up white phlegm is the cure for colds, and if coughing up yellow phlegm is wind-heat infection, we should pay attention to whether there are symptoms such as dizziness, fever and fear of cold. It is best to measure the temperature. After viruses or bacteria invade the respiratory tract, the bronchi secrete mucus, and after viruses or bacteria attach, the cilia of the bronchi move and cough to expel sputum. However, it is easy to get bad for a long time after catching a cold, so bacteria or viruses will invade the lungs, which will easily cause pneumonia, which will lead to aggravation of cough and excretion of phlegm from the lungs.