Causes

Interstitial lung disease seems to occur when an injury to your lungs triggers an abnormal healing response. Ordinarily, your body generates just the right amount of tissue to repair damage. But in interstitial lung disease, the repair process goes awry and the tissue around the air sacs (alveoli) becomes scarred and thickened. This makes it more difficult for oxygen to pass into your bloodstream.

Interstitial lung disease can be triggered by many different things — including airborne toxins in the workplace, drugs and some types of medical treatments. In most cases, the causes are unknown.

Occupational and environmental factors

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

• Silica dust
• Asbestos fibers
• Grain dust
• Bird and animal droppings
• Radiation treatments
• Indoor hot tubs

Some people who receive radiation therapy for lung or breast cancer show signs of lung damage months or sometimes years after the initial treatment.

Medications

Many drugs can damage your lungs, especially:

• Chemotherapy drugs. Drugs designed to kill cancer cells, such as methotrexate (Otrexup, Trexall, others) and cyclophosphamide, can also damage lung tissue.
• Heart medications. Some drugs used to treat irregular heartbeats, such as amiodarone (Nexterone, Pacerone) or propranolol (Inderal, Innopran), may harm lung tissue.
• Some antibiotics. Nitrofurantoin (Macrobid, Macrodantin, others) and ethambutol (Myambutol) 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 autoimmune diseases such as:

• Rheumatoid arthritis
• Scleroderma
• Dermatomyositis and polymyositis
• Mixed connective tissue disease
• Sjogren's syndrome
• Sarcoidosis

The list of substances and conditions that can lead to interstitial lung disease is long. Even so, in some cases, the causes are never found. Disorders without a known cause are grouped together under the label of idiopathic interstitial pneumonias, the most common and deadly of which is idiopathic pulmonary fibrosis.