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Idiopathic Pulmonary Fibrosis (IPF) Overview

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This information was reviewed and approved by Jeffrey James Swigris, DO, MS (9/1/2017).

What is Idiopathic Pulmonary Fibrosis or IPF?

Interstitial lung disease (ILD) is a broad category of lung diseases that includes more than 200 disorders that can be characterized by fibrosis (scar) and/or inflammation of the lungs.

Despite an exhaustive evaluation, in many people the cause of ILD remains unknown. In these cases, the ILD is considered “idiopathic” (meaning of unknown cause).


Idiopathic pulmonary fibrosis is a term used to refer to one particular form of pulmonary fibrosis of unknown cause. Idiopathic pulmonary fibrosis is commonly called IPF.

Let’s take a look inside the lungs to see what is happening with IPF.

In IPF, scarring or fibrosis occurs in the interstitium. The interstitium of the lung refers to the microscopic area within the walls of the alveoli (air sacs). Like the leaves on a tree, the alveoli arise from the tiniest bronchioles (airways).

There are hundreds of millions of alveoli in a lung: 150 alveoli would fit in a cubic millimeter. Each alveolus (individual air sac) is surrounded by a network of tiny blood vessels (capillaries) — like mesh encircling the alveolus. The air sac and blood vessels together are called a respiratory unit. This is where the exchange of oxygen and carbon dioxide take place. In IPF, scarring or fibrosis disrupts the interstitium; the air sac wall thickens; oxygen cannot pass into the bloodstream as it normally should; and the lungs get stiff and difficult to expand.