Interstitial lung diseases are a group of conditions that lead to progressive scarring (fibrosis) of the lung tissue, particularly affecting the interstitium, the space around the alveoli (air sacs). These scars cause the lungs to become stiff, making it difficult to breathe and supply oxygen to the bloodstream. Causes can include long-term exposure to pollutants such as asbestos or silica, autoimmune diseases, infections, or certain medications.