Our lungs are one of the most vulnerable parts of the body, and the immune system is forever working hard to clear out the gunk and germs we breathe in every day, especially the smokers. Coughs come and go, but a cough that won't shift should not be passed off as normal.  A dry, tickly cough may be caused by a reaction to cholesterol-lowering drugs, acid from the stomach or mild asthma. A cough that goes on for two weeks or brings up blood should always be assessed by a doctor.  Smokers and ex-smokers need to be especially conscious of getting long-standing coughs checked out without delay.