A "smoker's cough" occurs when the irritants in smoke provoke the protective mechanisms of the air passages and the lungs. Smokers also tend to cough when they get up in the morning but this has a slightly different cause. This is because the tiny hair-like cilia that line the airways have been working while they slept to clear the lungs of the debris left by the previous day's smoking. The cilia are usually unable to clear the lungs during the day because they are anaesthetized by cigarette smoke. If the cilia are exposed to cigarette smoke over a long period of time then they may cease to function at all. Without the cilia to keep foreign matter from the lung the smoker's lung are at a much greater risk of damage.