What is Interstitial Lung Disease (ILD)? The lungs contain tiny air sacs (alveoli) where oxygen is absorbed. These air sacs expand with each breath. The tissue around these air sacs is called the interstitium. In people with interstitial lung disease, tissues become stiff or scarred, and the air sacs cannot expand as much. As a result, the body does not have sufficient oxygen. ILD causes scarring (fibrosis) of the lungs, and fibrosis causes stiffness in the lungs.  Scarring makes it difficult to take a breath because the lungs do not get sufficient oxygen. In ILD, the cells surrounding the alveoli (air sacs) are damaged, causing widespread inflammation and fibrotic scarring of the lungs. Damage to the lungs due to ILD is irreversible, however, further progression may be reduced with the treatment. Interstitial lung disease is also called diffuse parenchymal lung disease (DPLD) because the ILD affects the parenchymal tissues of the lungs. The Lung parenchyma includes the alveoli, th...