There are 4 pairs of sinuses connected to the nasal cavity by small openings. Normally air passes in and out of the sinuses, and mucus and fluid drain from the sinuses into the nose. Chronic sinusitis is much less common than acute sinusitis . It affects approximately 1 out of 1,000 people.
Some people never get sinusitis, and others develop sinusitis frequently.
When sinusitis recurs frequently, or lasts for a prolonged period of time, it is classified as chronic. Chronic sinusitis may have less severe symptoms than acute sinusitis, and it may therefore go untreated for long periods of time. This can cause damage and destruction to the tissues of the sinuses. Chronic sinusitis may flare up spontaneously or may follow respiratory infections such as colds . Sinusitis occurs when there is an undrained collection of pus in one or more of the sinuses.