The air we normally breathe enters the body through the trachea and bronchi, which are covered with very fine hairs called "strands. These fine hairs serve the function of attaching debris that enters with the air and sending it back to the upper part of the throat. Sometimes, however, the hairs do not work properly, and debris remains stuck to the hairs. When this happens, the brain sends an order to blow the debris away with a strong breath. This is coughing.

Coughing can occur even when there is no debris attached. This is the case with a disease called "asthma," which is caused by the brain giving orders to the body to cough even though there is no debris attached to the body.