Any cough that lasting more than 3 weeks needs to be examined by a Pulmonologist. They are many causes for this chronic cough. It can be due to a simple allergic irritation of nostril/sinuses or acid reflux from stomach to larynx to more complicated diseases like Tuberculosis, lung cancer etc. Tests that is needed to differentiate these diseases ranges from Chest X ray, Spirometry, Sputum exam, CT scanning of Chest (HRCT), CT sinuses, allergy testing, Bronchoscopy and upper gastro intestinal endoscopy. The most common Allergic rhinitis can be treated by allergen avoidance, controler medicine and or allergy Immunotherapy.
