Clinically, the human body feels phlegm in the lungs during breathing, and this manifestation is considered to have an inflammatory reaction of the respiratory tract. More commonly, the respiratory tract is invaded by pathogens, and there is congestion and edema of the mucous membrane, with a large amount of exudation of inflammatory material secretions. For example, inflammation caused by viruses, bacteria, mycoplasma, chlamydia, rickettsia, fungi, and even Mycobacterium tuberculosis infection. It is also seen in non-infectious lung diseases, such as bronchial asthma, where there is a large amount of inflammatory secretions from the airways, as well as bronchiectasis from various causes. In this case, an X-ray, CT or MRI of both lungs can be taken to clarify the diagnosis and early treatment can be given.