Definition of Idiopathic pulmonary fibrosis:

Idiopathic pulmonary fibrosis is scarring or thickening of the lungs without a known cause.

Causes, incidence, and risk factors:

No one knows what causes pulmonary fibrosis or why some people get it. It causes the lungs to become scarred and stiffened. This stiffening may make it increasingly difficult to breathe. In some people the disease gets worse quickly (over months to a few years), but other people have little worsening of the disease over time.

The condition is believed to result from an inflammatory response to an unknown substance. "Idiopathic" means no cause can be found. The disease occurs most often in people between 50 and 70 years old.