Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pulmonary Fibrosis ?
    ### Response:
    Pulmonary fibrosis is a condition in which the tissue deep in your lungs becomes scarred over time. This tissue gets thick and stiff. That makes it hard for you to catch your breath, and your blood may not get enough oxygen.    Causes of pulmonary fibrosis include environmental pollutants, some medicines, some connective tissue diseases, and interstitial lung disease.
    