Nasal drainage refers to any kind of matter that drains from the nose or nasal passages. It is generally some type of mucus and may be thick or thin, depending on the cause. Many different factors can cause mucus to flow, including allergies, viruses and injuries. The nose and sinuses may drain out the front of the nose or they may drain down the back of the nose and end up running down the throat in a condition called post-nasal drip.
One of the main functions of mucus in the body is to capture and remove harmful substances. This is why a person who has any kind of a virus will also typically have a runny nose. The body creates extra mucus and uses it to try to trap as many of the viruses as possible. Nasal drainage is the body’s way of removing the contaminated mucus from the body completely so that the virus cannot invade the lungs and other organs.
Infections caused by bacteria can also trigger nasal drainage. Bacteria that become trapped in the sinuses can cause such infections. The nasal passages become swollen and irritated and respond by increasing mucus production, which results in increased drainage as the passages are continually flushed out by the immune system.
Allergies are a very common causes of nasal drainage. People who are allergic to such things as pollen, dust or animal dander will get a runny nose whenever they are exposed to these things. This happens because the allergic reaction triggers the body’s protective mechanisms and the allergens are treated in the same way as germs and viruses.
Other conditions can also cause nasal drainage. When a person cries, the tears mix with the mucus inside of the nose, resulting in a drippy, runny nose. Very cold weather may cause nasal drainage as the body tries to warm the air entering through the nose. The flow of blood to the inside of the nose is increased, warming the air but also causing the body to produce more mucus, resulting in a runny nose.
Most of the time nasal drainage is not serious and clears up on its own. In some cases antibiotics or antihistamines may be required to resolve serious or chronic conditions, but usually the drainage stops when the cause goes away. The exception to this is nasal drainage caused by a severe blow to the head, since in this case the runny nose could actually be the fluid leaking from areas around the brain. Such a condition must be treated immediately to prevent serious complications.