Cough is areflex phenomenon whenever there is a irritation in the respiratory tract. it may be manifestation of simple disease like allergy bronchitis to more severe pneumonia tuberculosis and eventually fatal disease like lung cancer in some it could be psychological ie where there is no other cause

THERE ARE SEVERAL CAUSES FOR COUGH:

Smoking :Smoking can cause a cough that doesn't go away. If you smoke, you need to stop. Talk to your doctor about using nicotine patches, gum, inhaler or nasal spray, or another method to stop smoking.

Allergies :Postnasal drip caused by allergies can make you cough. Postnasal drip is mucus that runs down your throat from the back of your nose. If you have postnasal drip from allergies, try to avoid the things you are allergic to, such as the following:
Dust
Smoke
Pollen, mold, and freshly cut grass
Pets and certain plants
Cleaning agents and room deodorizers ...more

Throat infection
have honey

Due to alergy

They r sick