What is a runny nose?
A runny nose is mucus being discharged, or “running,” or dripping, out of the nose. It can be caused by colder outdoor temperatures, or by the cold, flu, or allergies.
When a cold virus or an allergen, such as pollen or dust, first enters the body, it irritates the lining of the nose and sinuses, or air-filled pockets around the face, and the nose starts to make a lot of clear mucus. This mucus traps the bacteria, virus, or allergens and helps flush them out of the nose and sinuses.
After 2 or 3 days, the mucus may change color and become white or yellow. Sometimes the mucus may also turn a greenish color. All of this is normal and does not mean an infection is present.
How does the nose work to protect the body?
The breathing process starts in the nose. Air gets into the lungs through the nose. It helps filter, humidify, warm, or cool the air that comes through it, so that the air that gets to the lungs is clean.
A special lining of mucosa, or a moist tissue, covers the area inside the nose and consists of many mucus-producing glands. As bacteria, allergens, dust, or other harmful particles come into the nose, the mucus traps them. Mucus contains antibodies, or enzymes, which kill unwanted bacteria and viruses.
The mucosa lining also includes cilia, or tiny hair-like structures. The cilia are continually in motion and move the collected harmful particles and the mucus that they are trapped in through the nose into the back of the throat. It is then swallowed and destroyed by the acid in the stomach. Mucus and particles can also be coughed up or sneezed out.
When outdoor temperatures turn cold, the pace of this process slows down. Many times, the mucus stays in the nose and then drips or dribbles out of the nose.
Why is mucus an important part of the airway system?
Mucus production is a normal and necessary part of the airway system. Mucus is needed to keep the airway moist and working properly. Not only does mucus stop harmful particles from getting into the lungs, but it also contains antibodies to help destroy bacteria. If too much mucus is produced, the body wants to get rid of it, leading to coughing and spitting the extra mucus out, and blowing it out of the nose.