Smoker's lungs. Conceptual image of a smoker's lungs, with smoke rising from the trachea (windpipe). Cigarettes contain cancer-causing chemicals and the addictive drug nicotine. Tobacco smoke is the major cause of lung cancer and several other lung diseases. Shown here are patches of diseased lung (green), which could represent malignant tumours or emphysema, a disorder where the air sacs in the lungs become enlarged and damaged reducing the surface area for the exchange of oxygen and carbon dioxide.