Every day, glands in the lining of your nose, throat, airways, stomach, and intestinal tract produce about 1 to 2 quarts of mucus -- a thick, wet substance that moistens these areas and helps trap and destroy foreign invaders like bacteria and viruses before they can get into your body and cause infection. Normally, you don't notice the mucus from your nose because it mixes with saliva and drips harmlessly down the back of your throat to be swallowed gradually and continuously throughout the day.
Only when your body produces more mucus than usual or the mucus is thicker than normal does it become more noticeable. Excess mucus can come out the front of your nose in the form of a runny nose. When the mucus runs down the back of the nose to the throat, it's called postnasal drip.
Deviated septum (abnormal placement of the wall that separates the two nostrils) or another anatomical problem that affects the sinuses
Changing weather fronts, cold temperatures, or excess dryness in the air
Certain foods (for example, spicy foods may trigger mucus flow)
Fumes from chemicals, perfumes, cleaning products, smoke, or other irritants
Sometimes the problem is not that you're producing too much mucus, but rather that it's not being cleared away effectively. Swallowing problems can cause a buildup of liquids in the throat, which can feel like postnasal drip. These problems can sometimes occur with age, a blockage, or conditions such as gastroesophageal reflux disease (GERD).
Symptoms of Postnasal Drip
Postnasal drip creates an annoying feeling that makes you want to constantly clear your throat. Because the feeling of the liquid in your throat is irritating and contains inflammatory substances, postnasal drip also can trigger a cough, which often gets worse at night. In fact, postnasal drip is the most common cause of chronic cough. Excess mucus running down your throat may also make you feel hoarse and give you a sore throat.
If the mucus plugs up the Eustachian tube -- the tube that connects the throat to the middle ear -- it can lead to a painful ear infection. When mucus blocks the sinus passages, it can lead to a sinus infection.