why do we cough during sick with a cold?

Answer 1

It is the body's natural way of eliminating an irritating substance from your windpipe/lungs. The cold virus within your windpipes is irritating your surroundings, and your body is attempting to eliminate it. Often allergies and dust trigger the same reactions.

This is also the most common way a cold spreads from one person to another. Because a cold that causes you to cough is one that is more likely to spread, there is a better chance that the one you contract is one that's likely to irritate your throat.

The following source page explains it in detail:
http://www.drreddy.com/rhinitis.html

Hope this helps,
Ken

Answer 2

Coughing is a normal function of the body whether we are sick or well. Coughing clears the airway of trapped debris (dust, bacteria, etc.) and the mucus produced by the membrane lining our respiratory system to trap debris.

Answer 3

thats the bodies way of trying to get rid of the foreign matter in the system. coughing, sweating, blowing your nose etc.