Idiopathic pulmonary fibrosis (IPF), or (formerly[5]) fibrosing alveolitis, is a rare, progressive illness of the respiratory system, characterized by the thickening and stiffening of lung tissue, associated with the formation of scar tissue. It is a type of chronic scarring lung disease characterized by a progressive and irreversible decline in lung function.[3][4] The tissue in the lungs becomes thick and stiff, which affects the tissue that surrounds the air sacs in the lungs.[6] Symptoms typically include gradual onset of shortness of breath and a dry cough.[1] Other changes may include feeling tired, and abnormally large and dome shaped finger and toenails (nail clubbing).[1] Complications may include pulmonary hypertension, heart failure, pneumonia or pulmonary embolism.[1] The cause is unknown, hence the term idiopathic.[2] Risk factors include cigarette smoking, acid reflux disease (GERD), certain viral infections, and genetic predisposition.[1] The underlying mechanism involves scarring of the lungs.[1] Diagnosis requires ruling out other potential causes.[3] It may be supported by a HRCT scan or lung biopsy which show usual interstitial pneumonia (UIP).[3] It is a type of interstitial lung disease (ILD).[3]

Reference
Wiki: Idiopathic pulmonary fibrosis