There are over 100 causes of pulmonary fibrosis. It may be caused by chronic infection, cancer, or long-term use of drugs. Examples of drugs that might cause it are anti-cancer drugs, hydralazine, nitrofurantoin, and drugs for rheumatoid arthritis. Other causes include long-term exposure to asbestos, beryllium, silica, and coal dust and sensitivity to proteins made by animals such as birds and rats.
Pulmonary fibrosis may be hereditary. There are two ways in which this may occur. One is that the condition is inherited and symptoms show up later in life, usually in the forties or fifties. Or children may inherit a tendency to be extra sensitive to the known causes of pulmonary fibrosis, such as asbestos. Therefore they may be more likely to develop the condition when they are exposed to these causes.
When the cause of the fibrosis is not known, it is called idiopathic pulmonary fibrosis.