ILD can have many causes. Sometimes the cause is known. In other cases, no cause can be identified. 

1. Idiopathic Pulmonary Fibrosis (IPF) 

When no cause for pulmonary fibrosis can be identified the disease is termed idiopathic pulmonary fibrosis or IPF. Idiopathic simply means ‘of unknown cause. This is the most common type of ILD/PF. This is the most common cause of fibrosis.

Risk Factors for Idiopathic Pulmonary Fibrosis (IPF)

Although IPF is a disease of unknown cause, there are a number of potential risk factors for the development of IPF that are known. They include: 

• Smoking Smoking increases the risk of lung damage and IPF. 
• Environmental Exposures Certain jobs and occupations such as farming, raising birds, hair dressing, and stone cutting/polishing may be connected. Contact with livestock and different kinds of dust (metal, wood, vegetable and animal) are also risk factors. 
• Viruses Some viral infections may play a role, but more research is needed. 
• Gastroesophageal Reflux Disease (GERD) GERD is a chronic digestive disease. GERD occurs when stomach acid or content flows back into your food pipe (esophagus). This backwash (reflux) irritates the lining of your esophagus and is what causes GERD. GERD may also be related to IPF, however, more research is still needed in this area. 
• Genetics Genetics can play a role in IPF. A very small percentage of people with IPF have reported two or more family members with the disease. 
• Gender IPF is more common in men than women. 
• Age IPF is more common in people 50 years and older. The risk increases with age. 

2. Autoimmune Disease 

Autoimmune diseases occur when the body’s immune system mistakenly attacks healthy tissue, thinking it’s a foreign invader. Some autoimmune disease linked to ILD include:  

• Rheumatoid Arthritis 
• Scleroderma 
• Systemic Lupus Erythematosus (SLE) 

Not everyone with these conditions develops pulmonary fibrosis, but the risk is higher than someone without an autoimmune disease.

3. Occupational/Environmental Exposures  

Breathing in certain dusts or chemicals over time can damage the lungs. Examples include: 

• Coal dust (coal workers’ pneumoconiosis)
• Silica dust (silicosis)
• Asbestos (asbestosis)
• Metal, wood, vegetable, or animal dust 
• Exposure to livestock or birds 
• Certain chemicals or inhaled drugs such as cocaine, zinc chloride, and ammonia

Some jobs that may increase risk include: 

• Farming 
• Bird handling or raising birds 
• Hairdressing 
• Stone cutting or polishing 
• Long-term exposure increases the risk of lung scarring. 
• Medical tests and treatments  

Certain medication and treatment exposures can cause lung scarring. These may include:  

• Certain chemotherapy medications  
• Some antibiotics  
• Some anti-inflammatory medications 
• Radiation therapy to the chest  

If you are concerned about medications affecting your lungs, speak with your healthcare provider. 

4. Cystic or Airspace Filling

These are considered ILDs because they affect the lungs’ gas-exchanging areas. Some ILDs cause inflammation or scarring, while others cause cysts or fill the air sacs with material.

• Cystic ILD = abnormal air-filled spaces, or cysts, form in the lungs. The cysts can damage lung tissue and make breathing harder.
• Airspace-filling ILD = the air sacs become partly filled with fluid, protein, blood, or inflammatory cells, instead of air. This makes it harder for oxygen to move from the lungs into the blood.

5. Sarcoidosis

Sarcoidosis causes clusters of inflamed cells, called granulomas, to form in the lungs. These granulomas can inflame and stiffen the lung tissue, narrow the airways, and reduce oxygen exchange. Over time, ongoing inflammation may lead to permanent scarring, or fibrosis, resulting in ILD.

6. Others

Familial Pulmonary Fibrosis (FPF) 

• Also known as genetic pulmonary fibrosis, FPF is typically recognized when two or more biological family members have pulmonary fibrosis. 
• FPF is strongly linked to inherited gene mutations, but not everyone who carries the mutation will develop PF. 
• The gene-environment (for example: smoking, exposure, autoimmune condition) interaction contributes to disease development, not simply genetics alone.