A cough can be classified based on how long it lasts:
--Acute cough lasts for 3 weeks or less. Common causes of an acute cough include the common cold, flu, and pneumonia.
--Subacute cough lasts 3 to 8 weeks. Common causes of a subacute cough include bacterial infection of the sinus.
--Chronic cough lasts more than 8 weeks. Common causes of a chronic cough include smoking, asthma, and gastroesophageal reflux disease (when acid from your stomach goes back up towards your throat).