The sinuses are passages around your nose and forehead that help keep the nasal passages clean so dust, bacteria and other material doesn't enter your body through your nose. Like the nasal passages, your sinuses produce a steady flow of mucus. While most people generally don't notice it, that mucus drains into the back of the throat, where it is usually swallowed so stomach acids can destroy the bad bacteria. However, sometimes the drainage will increase or thicken, suddenly becoming all too noticeable. This is often called post-nasal drip. Many people have other symptoms along with the excess drainage.
Sinus Drainage and Allergies
If you have allergies, you may occasionally experience post-nasal drip. You may also have itchy or watery eyes, and some people have ear problems. While your mucus may be quite thin initially, because the sinuses swell, an untreated allergy with excess mucus production could lead to a bacterial infection if the passages become blocked and unable to drain properly.
Sinus Drainage and Infection
Sinusitis, or inflammation of the sinus, is frequently due to an infection. It can be acute or chronic, but in both cases, the mucus drainage is usually thick, and sometimes either yellowish or greenish in color. You may also feel pressure or get a headache in your forehead, cheeks or around your eyes. You may also have a fever or a cough and feel tired; your teeth may hurt, or your sense of smell could be affected, or you may have bad breath.
Other Sinus Irritants
Tobacco smoke, air pollution and other irritants can also lead to post-nasal drip. Dry air may also be a problem, because the mucus becomes too thick. Symptoms that accompany post-nasal drip from irritants are similar to those of infection, because the irritants generally limit good sinus drainage.
Nose and Swallowing Disorders
If you have polyps or a deviated septum in your nose, it will also restrict sinus drainage, leading to thickened mucus and chronic sinusitis. Some people also have trouble swallowing, which means the mucus that usually is swallowed unconsciously may collect in the back of your throat. People who have trouble with swallowing may cough or clear their throats often, or be hoarse.