Pulmonary fibrosis is caused by scarring and thickening of the lung tissue, which can result from various factors. Causes include inhalation of environmental pollutants (such as asbestos, silica, coal dust), certain medications (e.g., amiodarone, bleomycin), radiation therapy to the chest, autoimmune diseases (e.g., rheumatoid arthritis, scleroderma), infections, and exposure to allergens like mold or bird droppings. In many cases, however, the exact cause is unknown, and this is referred to as idiopathic pulmonary fibrosis. Genetic factors may also play a role in susceptibility to the disease.