A cough is basically a reflex action so the airways can be cleared of phlegm, mucus and other irritants like dust and smoke. An inflammation of the upper respiratory tract due to a virus could also cause a cough.

Coughing can be symptomatic of many conditions including bronchitis, asthma, the common cold, flu, whooping cough or smoking. There are even some prescribed medicines that can cause coughing such as ACE-inhibitors which are used to treat heart failure.

Sometimes a cough can be a symptom of an underlying serious medical condition such as heart failure, lung cancer, tuberculosis, pneumonia or a pulmonary embolism (which is a clot on the lung). Coughs that have been caused by things like flu or the common cold normally disappear after a few days, but coughs that have been caused by an infection of the lung, such as bronchitis, could persist for several weeks, even after the infection has cleared up and this is due to the inflammation of the airways which usually take a while to clear up.

Cough Mechanism and Receptors

If someone has been suffering from a cough for more than a couple of weeks after having a viral infection, they should go to their doctor for medical advice.