Why do we cough? And what is phlegm?

As long as they are healthy, our respiratory passages clean themselves. A protective mucous layer captures tiny foreign bodies (e.g. dust, pollen or germs) like a net, while tiny hairs - the cilia - constantly move the mucus, together with the foreign bodies, toward the mouth.

At times, however, larger foreign bodies - such as breadcrumbs or drops of a drink - penetrate into our respiratory tract.

Then the cilia and the mucous layer are overtaxed, and we have to cough: We take a lot of air into the lungs, our chest muscles suddenly contract, and both air and foreign bodies are expelled. In this way, coughing helps to clear the bronchi.

Coughing may also be a symptom of an infection of our respiratory tract. If our immune system is weakened, viruses or bacteria can lodge in the respiratory passages, and to fight them off more mucus is produced.

This mucus (known as phlegm) is thicker and stickier than normal mucus, and sticks deep in our bronchi. The body is unable to eliminate the mucus in the usual gentle way.

Therefore we try to loosen this phlegm with the cough. If the mucus is not expelled properly, it can build up and become more and more viscous (i.e. thick and sticky).

This can lead to an unpleasant and troublesome cough, in which the cilia are coated with viscous phlegm and are unable to properly move the mucus out of the respiratory tract.


Information Source: http://www.bisolvon.com/com/Main/cough/clinical/index.htm