Fibrous streaks in the lungs may be associated with pneumonia, old tuberculosis, idiopathic interstitial fibrosis and other causes. 1. Pneumonia: When pneumonia occurs, as the lesions formed by pneumonia cannot be completely absorbed, fibrous tissue will be produced to gradually replace the lesions of pneumonia, thus forming a fibrous streak shadow. 2. Old tuberculosis: after regular treatment of tuberculosis, the tuberculosis foci are replaced by fibrous tissues during the healing process of tuberculosis, resulting in fibrous streaks in the lungs when chest x-ray examination is performed. 3. Idiopathic interstitial pulmonary fibrosis: refers to diffuse inflammatory disease of the lower respiratory tract of unknown cause. Inflammation invades the alveolar walls and adjacent alveolar cavities, causing thickening of the alveolar septa and pulmonary fibrosis. Fibrous streaks in the lungs are more widely involved and often irreversible damage. Therefore, early medical attention is recommended. When streak shadows are detected in the lungs, it is recommended to go to the hospital regularly for review and recheck to detect any changes in the disease in time for timely treatment.