Postnasal drip is extra mucus felt in the back of the nose and throat caused by the glands in these areas. People with postnasal drip usually feel they have to clear their throat more than normal.
The nose, throat, and sinuses ar all perpetually producing mucous secretion. Mucus is a thick and slippery substance that helps to keep the airways from drying out throughout the day.
The air people breathe is full of germs, pollen, and other environmental pollutants. When the air enters the body, these particles can create problems if they are not filtered out. It is the job of mucus to trap these foreign bodies and help eliminate them.