There are four sinuses on each side of our head. They are the maxillary, ethmoid, frontal and sphenoid sinuses. The primary purpose of the sinuses is to moisten and filter the air we breathe. The sinuses secrete mucous that is swept into the back of our throats taking with it any dust, pollens, bacteria or viruses that have been filtered. Disruptions in this process cause sinus infections, sinus headaches, facial pain, nasal congestion, post nasal drainage and a host of other problems.