It is the process of releasing air through the windpipe and mouth in a sudden noisy manner. Cough is initiated when there is a mechanical or chemical irritation to bronchi and trachea or by pressure from adjacent structures. Larynx and carina are especially sensitive to chemical stimuli such as SO2 gas or chlorine gas.
It is a physiological mechanism which:
1. Clears the respiratory pathways from foreign materials and extra secretions
2. May help to prevent sudden collapse of lungs.