The inner surface of the respiratory tract is covered in ciliated epithelium. It is a thin tissue that contains small, hair-like structures. These hairs, known as cilia, move back and forth to help move particles out of our body. The particles adhered to the mucus are transported backwards in the nasal cavity and upwards into the pharynx. From the throat, the mucus is swallowed and transported to the stomach, where stomach acids kill impurities.

The sense of smell in your nose constantly monitors the air quality. The nose is also sensitive to larger impurities and itching. We tend to remove impure particles by sneezing them out. Coughing is often the deliberate removal of impurity from the trachea.

During swallowing, the epiglottis closes to prevent parts of food from entering into the lungs. If we try to talk and eat at the same time, closing the epiglottis is impossible, because speaking requires air to be exhaled from the lungs. From early childhood, we are told not to talk with food in our mouths.

The bronchi and lungs are sensitive to cold, so it is advisable to preheat the air before it reaches the lungs. This happens automatically as the air passes through the moist and warm tract.

Pollen particles cause allergic reactions in many people. Many foreign substances and impurities remain in the nasal mucosa.