The nose normally produces mucus to trap substances (like dust, pollen and pollution) and germs (bacteria and viruses). Mucus flows from the front of the nose and drains down the back of the throat. When too much mucus is made, it can cause a runny nose from the front or post-nasal drip from the back. Coughing is the natural response to clearing the throat from post-nasal drip.
Itching, sneezing, and other symptoms can be responses to:
- Allergic reactions
- Chemical exposures including cigarette smoke
- Temperature changes
- Other factors
In most people, nasal congestion moves from one side of the nose to the other over the course of several hours. Some people may notice this nasal cycle more than others, especially if their nasal passages are narrow. Strenuous exercise or changes in head position can affect nasal congestion. Severe congestion can result in facial pressure and pain, as well as dark circles under the eyes.