Pulmonary fibrosis, meaning scarring in the lung tissue, is an umbrella term for more than 200 different lung diseases that all look very much alike. In pulmonary fibrosis, the scar tissue builds up in the walls of the air sacs of the lungs, and eventually the scar tissue makes it hard for oxygen to get into your blood. Low oxygen levels (and the stiff scar tissue itself) can cause you to feel short of breath, particularly when walking and exercising. The most common symptoms of pulmonary fibrosis are cough and shortness of breath. Symptoms may be mild or even absent early in the disease process. As the lungs develop more scar tissue, symptoms worsen. This can typically be managed with medications to relax the lung tissue and limit the development of more scar tissue. However, if the disease progresses, lung transplant may be necessary.