Pulmonary receptors (cough receptors) in the epithelium of the respiratory tract are sensitive to both mechanical and chemical stimuli. The bronchi and trachea are so sensitive to light touch that slight amounts of foreign matter or other causes of irritation initiate the cough reflex.

Infection, inflammation and irritants are the causes of a cough. If all these are not settled correctly, cough won't get settled. 

But a cough is good for your lungs, by coughing lungs relieves acute bronchospasm thereby increasing oxygen supply to the heart if a cough is persistent then its a sign of decreased oxygen intake.

Principles of reducing cough drink plenty of fluids, preferably hot, quit smoking, pepper has a good effect in reducing cough especially can take vegetable soups, if you use inhalers it will reduce a cough immediately, marshmallows, honey, mint and tulsi leaves will help relieve a cough.