Cough is due to failure of the lung to disperse and descend and upward adverse flow of pulmonary qi, usually seen in lung disorders. Cough may be caused by the disorders of other viscera. Cough is usually related to sputum. So in diagnosis, cares should be taken to analyze the characteristics of voice in cough, understand the time and duration of cough and differentiate the syndromes in the light of the color, nature and quantity of sputum as well as other complications.
 
Deep cough with whitish thin sputum and nasal obstruction is usually due to wind cold attacking the lung, or due to retention of pathogenic cold in the lung which prevents the lung from normal dispersing and descending. Low cough with profuse whitish sputum easy to expectorate accompanied by chest oppression and epigastric fullness is often due to stagnation of phlegm and dampness in the lung which stop the lung from normal dispersing and descending. Low cough with yellowish thick sputum easy to expectorate accompanied by dry pain of throat and hot sensation in the nose in breathing is due to invasion of pathogenic heat into the lung which consumes pulmonary fluid and inhibits flow of pulmonary qi.

Dry cough without sputum or with scanty and sticky sputum and dry throat is due to invasion of pathogenic dryness into the lung or due to deficiency of pulmonary yin, consumption of pulmonary fluid and failure of the lung to depurate and clear. Weak cough accompanied by shortness of breath or dyspnea is due to lung asthenia or due to consumption of pulmonary qi in chronic diseases.
 
Besides, cough like barking of a dog accompanied by hoarseness usually indicates diphtheria due to asthenia of lung and kidney yin, pestilent factors attacking the throat and obstruction of the airway. Infantile paroxysmal and continuous cough like the crying of an egret in the end is called "whooping cough" or "pertussis", usually caused by mixture of pathogenic wind with latent phlegm which transforms into heat and obstructs the airway.