A cough is a physical response to an obstruction of the windpipe or breathing passages, regardless of the cause of the obstruction.
The most common causes are colds, flu, and sinusitis, but coughing can also be triggered by the inhalation of dust, fumes, cigarette smoke, or small objects such as pieces of food.
If coughing persists over a long period of time, it can cause further irritation to the airways.
Many of the chronic respiratory diseases caused by smoking and industrial pollution (such as emphysema, chronic bronchitis and asbestosis) are characterised by deep coughing with thick mucus that is difficult to expel. Any persistent cough may be a symptom of an underlying illness - discuss your symptoms with your healthcare professional.