The sinuses are air-filled spaces located in the bones of the face and skull. They produce a thin layer of mucus that normally flows freely into the nose, moistening the air we breathe and fighting infection by trapping and removing inhaled pollutants such as dust, mold, viruses, and bacteria.

When the connections between the nose and sinuses become blocked, mucus cannot drain normally and infection or sinusitis often follows.

This type of obstruction occurs for various reasons:

• The most common cause is temporary swelling due to a cold or allergy
• Congenital narrowing of the sinus outflow tracts can contribute to repeated infection
• Abnormalities in the nose such as deviated septum or nasal polyps can also contribute to repeated infection

Additional factors that reduce the mucous membranes’ ability to fight infection include:

• Allergies to pollen, dust, animals and foods
• Exposure and sensitivity to mold
• Poor air quality
• Acid reflux from the stomach into the nose and sinuses
• Immune problems
• Severe systemic disease such as diabetes and cancer