Question: What causes sinus infections and what are the most common symptoms of sinus infections?
Answer: The sinuses are air-containing spaces in the bones of the face and the skull, and these spaces drain through little pinpoint openings into the nose. When they become blocked, mucus builds up inside the sinuses, bacteria overgrows in this mucus, and you develop pain or pressure -- typically, facial pressure when the cheek sinuses known as the maxillary become blocked, or headaches when the sinuses in the forehead known as the frontal sinuses become blocked.
So a primary symptom is that headache, or facial pain, or pressure. The second most common symptom of a sinus infection is congestion, or difficulty breathing through your nose. And the third most common symptom would be nasal drainage, particularly post-nasal drip, mucus that runs down the back of the throat.