<qa>  What is the most common type of fibrosis?Pulmonary fibrosis is essentially scarring in the lungs. Some types DIP, NSIP most often respond to therapy. Others like UIP usual interstitial pneumonitis rarely respond. UIP frequently progresses and has a poor prognosis with a survival of three to five years. In UIP, most often the cause cannot be determined and is therefore called Idiopathic Pulmonary Fibrosis IPF. A prevalence rate of 2729 cases100,000 has been reported that may even be as high as 250 cases100,000 in individuals 75 years of age. 