Lung nodules can be caused by many things, and most are not cancer. Common causes include old infections, inflammation, scar tissue, inhaled irritants like air pollution, and benign or cancerous tumors.

Common causes

  • Infections: Tuberculosis, pneumonia, and fungal infections can leave nodules behind.
  • Inflammation or autoimmune disease: Conditions such as rheumatoid arthritis and sarcoidosis may cause nodules.
  • Scar tissue: Healed lung injury or prior infection can show up as a nodule.
  • Irritants: Air pollution and other inhaled particles can contribute.
  • Benign growths: Some nodules are harmless tumors like hamartomas.
  • Cancer: Lung cancer can also appear as a nodule, especially when risk factors like tobacco smoke or radon exposure are present.

What matters most

A lung nodule’s cause depends on its size, shape, growth over time, and your risk factors. Many nodules are found incidentally on imaging and are monitored rather than treated right away.

When to get checked

If a nodule is new, growing, or you have symptoms like coughing up blood, unexplained weight loss, chest pain, or shortness of breath, it’s important to follow up with a clinician promptly.

If you want, I can also give you a simple “benign vs concerning lung nodule” checklist.