Smokers do not necessarily have nodules in their lungs, but the tar, heavy metals, nicotine and other substances in cigarettes are deposited in the airways and alveoli, and black mottled deposits can be found during bronchoscopy, and there are anatomical drawings showing that 15-year smokers have large black spots covering both lungs, while 30-year smokers have black lungs like splashed ink. The deposition of these harmful substances in cigarettes can damage the function of the airway ciliary epithelium, which leads to a decrease in the self-cleaning ability of the lungs, and the persistence of these harmful substances can stimulate the proliferation of lung tissue, so the chances of lung nodules and even lung cancer are much higher in smokers than in non-smokers.