Causes

Pulmonary fibrosis scars and thickens the tissue around and between the air sacs (alveoli) in your lungs. This makes it more difficult for oxygen to pass into your bloodstream. The damage can be caused by many different factors — including long-term exposure to certain toxins, certain medical conditions, radiation therapy and some medications.

Occupational and environmental factors

Long-term exposure to a number of toxins and pollutants can damage your lungs. These include:

• Silica dust
• Asbestos fibers
• Hard metal dusts
• Coal dust
• Grain dust
• Bird and animal droppings

Radiation treatments

Some people who receive radiation therapy for lung or breast cancer show signs of lung damage months or sometimes years after the initial treatment. The severity of the damage may depend on:

• How much of the lung was exposed to radiation
• The total amount of radiation administered
• Whether chemotherapy also was used
• The presence of underlying lung disease

Medications

Many drugs can damage your lungs, especially medications such as:

• Chemotherapy drugs. Drugs designed to kill cancer cells, such as methotrexate (Trexall, Otrexup, others) and cyclophosphamide, can also damage lung tissue.
• Heart medications. Some drugs used to treat irregular heartbeats, such as amiodarone (Cordarone, Nexterone, Pacerone), may harm lung tissue.
• Some antibiotics. Antibiotics such as nitrofurantoin (Macrobid, Macrodantin, others) or ethambutol can cause lung damage.
• Anti-inflammatory drugs. Certain anti-inflammatory drugs such as rituximab (Rituxan) or sulfasalazine (Azulfidine) can cause lung damage.

Medical conditions

Lung damage can also result from a number of conditions, including:

• Dermatomyositis
• Polymyositis
• Mixed connective tissue disease
• Systemic lupus erythematosus
• Rheumatoid arthritis
• Sarcoidosis
• Scleroderma
• Pneumonia

Many substances and conditions can lead to pulmonary fibrosis. Even so, in most cases, the cause is never found. Pulmonary fibrosis with no known cause is called idiopathic pulmonary fibrosis.

Researchers have several theories about what might trigger idiopathic pulmonary fibrosis, including viruses and exposure to tobacco smoke. Also, some forms of idiopathic pulmonary fibrosis run in families, and heredity may play a role in idiopathic pulmonary fibrosis.

Many people with idiopathic pulmonary fibrosis may also have gastroesophageal reflux disease (GERD) — a condition that occurs when acid from your stomach flows back into your esophagus. Ongoing research is evaluating if GERD may be a risk factor for idiopathic pulmonary fibrosis, or if GERD may lead to a more rapid progression of the condition. However, more research is needed to determine the association between idiopathic pulmonary fibrosis and GERD.