productive cough

A productive cough is one that brings up sputum — phlegm coughed up from the airways — as opposed to a dry cough, which produces nothing. It is the airway's clearance mechanism in action: when mucus and debris build up, a forceful cough propels them up and out so they can be swallowed or spat.

What is coughed up carries useful clues. Clear or white sputum is common in ordinary viral infection or stable chronic bronchitis; thick yellow or green sputum often reflects a heavier load of inflammatory cells, which may but does not always mean bacterial infection; rusty or blood-tinged sputum, and large daily volumes, each point in particular directions. The amount, color, smell and consistency are all noted and a sample can be sent for laboratory testing.

A productive cough lasting only days usually accompanies acute bronchitis or a chest infection and settles as the illness resolves. A cough productive of sputum on most days for three months in two consecutive years is the working definition of chronic bronchitis, often from smoking. Daily large-volume, sometimes foul, sputum suggests bronchiectasis. The pattern over time, rather than any single cough, guides the diagnosis.