Although mucus normally is swallowed unconsciously, the feeling that it is accumulating in the throat or dripping from the back of your nose is called post-nasal drip. This feeling can be caused by excessive or thick secretions or by throat muscle and swallowing disorders. Increased thick secretions in the winter often result from too little moisture in heated buildings and homes. They can also result from sinus or nose infections and some allergies, especially to certain foods such as dairy products. If thin secretions become thick and green or yellow, it is likely that a bacterial sinus infection is developing.
Sinuses are air-filled cavities in the skull.
They drain into the nose through small openings. Blockages in the openings from swelling due to colds, flu, or allergies may lead to acute sinus infection. With this infection you may notice increased post-nasal drip. If you suspect that you have a sinus infection, you should see your physician for antibiotic treatment. Chronic sinusitis occurs when sinus blockages persist and the lining of the sinuses swell further.