Why is it that smokers get more lung infections?

It is poison to lung: Various elements in cigarette smoke damage the cells which line the air passages and the alveolar cells in the lungs where oxygen is absorbed. It especially damages the hair cells which have little cilia which push mucus and the crud we breathe in out of the lungs, so our lungs cannot clean themselves out. It also kills immune cells which help produce antibodies and kill the germs we are breathing.