Under normal conditions, the lungs and sinuses secrete a thin, protective layer of mucus that traps dust and other particles in the air. Cilia, which are thin, hair-like projections, sweep this mucus to the back of the throat (from the sinuses) or to the top of the throat (from the lungs). When mucus becomes trapped in the lungs and the cilia are unable to move it out, an involuntary, explosive expulsion of air from the lung occurs in an attempt to expel the mucus and irritants.
All over-the-counter cough medicines contain cough suppressants, which suppress this cough reflex. This does not help the body eliminate the irritants. Decongestants help thin the mucus so that it can move more freely and expectorants stimulate the cilia to move it out of the system. The following herbs act as expectorants and decongestants to help make coughs productive.