A persisting cough always has a cause. Most commonly the cause is an acute respiratory infection, and the cough lasts for a few days or maybe a few weeks. When the cough lasts longer, something else is going on. And smoking is often that something else. A cough associated with an uncomplicated chest cold seldom lasts for more than three weeks in a non-smoker.
Smoking prevents healing of the inflamed air passages and results in continuing troubles.
Persistent coughing is often present in chronic diseases of the lung such as asthma, emphysema and cigarette smokers bronchitis. Persons with these ailments most often have experienced difficulties for many years and understand the nature of the cough. Asthma sometimes presents as a nagging cough, with little wheezing or breathlessness being noticed by the patient. And asthma can have its start at any age. Lung cancer is the most feared cause of a persisting cough.