ILD or Interstitial lung disease is a term that describes a large group of respiratory disorders. It is also known as diffuse parenchymal lung disease (DPLD). Most of these disorders cause progressive scarring (fibrosis) or inflammation of the interstitium. Interstitium is the tissue and surrounding space around the alveoli (air sacs) of the lungs. When there is scarring of the interstitium, it causes stiffness of the lungs, and the air sacs cannot expand fully. This affects the ability to breathe, and as a result, less oxygen enters the bloodstream.