Cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles, and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three phases: an inhalation, a forced exhalation against a closed glottis, and a violent release of air from the lungs following the opening of the glottis, usually accompanied by a distinctive sound. Coughing can have causes that aren't due to underlying disease. Examples include normal clearing of airways, irritants such as smoke and gas, tobacco use or improperly swallowing food and liquids.