A cough may be triggered by a tickle of dust or water that goes down the wrong way. Suddenly the muscles of your throat and chest contract and expel the invader in a rush of air and mucus at speeds approaching 600 m.p.h. This reflex actually originates in a special cough center in the brain. Coughs are almost always symptoms of a larger problem. Those coupled with a runny nose or fever point to a respiratory tract infection or more serious disease.
Productive coughs bring up mucus, often generated by a bacterial or viral infection.
Lining your bronchial tubes are mucous glands and small hairs called cilia. Normally, the glands secrete a little mucus to help catch debris when you're breathing, and the cilia help brush it all out. Dry coughs, as they are also sometimes called, are usually chronic and can be caused by asthma, smoking, allergies or congestive heart failure. It's always best to ask your doctor about medications. But in general, an expectorant cough medicine is used to help thin mucus so it can be cleared more easily from your lungs.