Sinus problems which have become chronic may be caused by injury of the nasal bones, smoking, small growths in the nose, or irritant fumes and odors. An over-acid condition in the stomach can cause sinus troubles. Poor digestion of starch, sugar, and dairy products can produce a runny nose. When force is used in blowing the nose, phlegm is pushed up into the sinuses. Swimming or diving can force phlegm up into the sinuses.
Allergic rhinitis is a common cause of sinusitis.
Avoid substances which might be giving you allergies. Decayed teeth, enlarged and infected adenoids, cigarette smoke, perfume, household cleansers, and dusty air can cause irritation to the sinuses. So sinus trouble can either be caused by an infection or by other things. If drainage is clear and there are no accompanying symptoms of a common cold, you probably have an allergy. If left untreated, this can lead to bronchitis, asthma, throat infection, or pneumonia.