Pulmonary fibrosis is a chronic and progressive lung disease characterized by the thickening and scarring (fibrosis) of lung tissue, which over time, leads to serious breathing difficulties. This condition results from the replacement of normal lung tissue with scar tissue, which reduces the lungs' ability to transfer oxygen into the bloodstream.

As the lung tissue becomes more damaged and scarred, its elasticity is reduced, making it difficult for the lungs to expand and contract efficiently. This hampers respiration and significantly affects a person's quality of life.