Interstitial Lung Disease (ILD) is a general term that includes a variety of chronic lung disorders. When a person has ILD, the lung is affected in three ways.
1. The lung tissue is damaged in some known or unknown way.
2. The walls of the air sacs in the lung become inflamed.
3. Scarring (or fibrosis) begins in the interstitium (or tissue between the air sacs), and the lung becomes stiff. When scarring of the lung tissue takes place, the condition is called pulmonary fibrosis.

People with different types of ILD may have the same kind of symptoms but their symptoms may vary in severity. Their chest X-rays may look alike. Further testing is usually recommended to identify the specific type of ILD a person has. The terms interstitial lung disease, pulmonary fibrosis and interstitial pulmonary fibrosis are often used to describe the same condition. The course of these diseases is unpredictable, but can be deadly. If they progress, the lung tissue thickens and becomes stiff. The work of breathing then becomes more difficult and demanding. Some of the diseases improve with medication if treated when inflammation occurs. Some people may need oxygen therapy as part of their treatment.

The diseases may run a gradual course or a rapid course. The condition may remain the same for long periods of time or it may change quickly. It's important to stay in touch with your doctor and report any changes in symptoms. You and your doctor can work together to manage ILD.

Fibrosis, or scarring of the lung tissue, results in permanent loss of that tissue's ability to transport oxygen. The level of disability a person experiences is directly related to the amount of tissue scarring.

Several causes of pulmonary fibrosis are known. They include:

• Occupational and environmental exposures. Many jobs exposing workers to asbestos, silica or metal dusts can cause pulmonary fibrosis. Some organic substances, such as moldy hay, cause an allergic reaction in the lung. This reaction is called Farmer's Lung and can cause pulmonary fibrosis. Other fumes found on farms are directly toxic to the lungs.
• Sarcoidosis. A disease characterized by the formation of granulomas (areas of inflammatory cells), which can attack any area of the body but most frequently affects the lungs.
• Drugs may have the undesirable side effect of causing pulmonary fibrosis.
• Radiation, as a result of treatment for breast cancer, for example.
• Connective tissue or collagen diseases such as rheumatoid arthritis and systemic sclerosis.
• Genetic/familial cause is possible, but less common than the others.
• Idiopathic Pulmonary Fibrosis (IPF). This is when all known causes of interstitial lung disease have been ruled out. There are several theories as to what may cause IPF; including viral illness and allergic or environmental exposure (including tobacco smoke). These theories are still being researched. Bacteria and other microorganisms are not thought to be the cause of IPF.