Lung nodules can be caused by a variety of factors, including inflammation from infections or irritants, benign tumors, and cancerous growths. The most common causes of lung nodules are inflamed tissue due to an infection or inflammation (called granulomas) or benign lung tumors (such as hamartomas) . Other causes of noncancerous lung nodules include air irritants or pollutants, autoimmune diseases, fungal infections like histoplasmosis, respiratory system infections such as tuberculosis (TB), and scar tissue. Malignant lung nodules are the result of cancers that either start in the lungs or metastasize (spread) to the lungs from a cancer elsewhere in the body. Risk factors for lung nodules include smoking, exposure to asbestos, radon or secondhand smoke, and a family history of cancer. Most lung nodules are not cancerous, but all nodules should be carefully evaluated because lung cancer is the No. 1 cause of cancer deaths in U.S. adults. If you have a pulmonary nodule, your healthcare provider may want to perform additional tests to determine the cause and rule out lung cancer.