Pulmonary fibrosis is a condition in which the lungs become scarred over time. Symptoms include shortness of breath, a dry cough, feeling tired, weight loss, and nail clubbing. Complications may include pulmonary hypertension, respiratory failure, pneumothorax, and lung cancer.Causes include environmental pollution, certain medications, connective tissue diseases, infections (including SARS infections), interstitial lung diseases. Idiopathic pulmonary fibrosis (IPF), an interstitial lung disease of unknown cause, is most common. Diagnosis may be based on symptoms, medical imaging, lung biopsy, and lung function tests.There is no cure and there are limited treatment options available. Treatment is directed towards efforts to improve symptoms and may include oxygen therapy and pulmonary rehabilitation. Certain medications may be used to try to slow the worsening of scarring. Lung transplantation may occasionally be an option. At least 5 million people are affected globally. Life expectancy is generally less than five years.