Ground glass does not exist in density, generally should refer to the size. Ground glass is an imaging result obtained through CT examination. Ground glass size of 0.4cm may be caused by chronic pneumonia, interstitial pneumonia, etc.; it may also be the early stage of malignant tumors, such as the early stage of lung adenocarcinoma. 1. Pneumonia: mainly due to infection and inflammation, and inflammation repeatedly stimulates the lung tissue to appear inflammatory exudation, and the existence of ground-glass nodules will be found through imaging examination, and the ground-glass will gradually become smaller after standardized treatment. 2. Interstitial pneumonia: Inflammation and fibrosis occur in the interstitium of lungs caused by inhalation of dust, irritating toxic gases, etc. At the early stage of the disease, there may be a mild increase in density and cloudy density shadow in CT image. 3. Early stage of lung adenocarcinoma: Early stage of lung adenocarcinoma usually grows along the alveolar wall, the number of cancer cells is small, the alveolar wall is slightly thickened, the alveoli do not have obvious narrowing or collapsing, and the density of lung tissues in which the cancer cells are located is a little bit higher than that of the normal lung tissues, but there are still more gases contained in the lung tissues, which can be manifested as a small glassy shadow in the CT. If you find ground-glass shadow in lungs, you should have regular checkups, and if there is any change, you should consult doctor in time to clarify the cause of the disease, so as to avoid delaying the disease.