Swelling and irritation of the spaces inside the nose and head, also known as sinuses, due to allergies.

Allergic sinusitis is caused by an allergic response to a harmless outdoor or indoor substance the body sees as harmful, known as an allergen. Substances can include pollen; dust mites; or tiny flecks of skin shed by cats, dogs and other animals with fur or feathers, known as pet dander. The swelling and irritation block the sinuses.

Symptoms might include itchy, watery eyes or sneezing. A person might have a stuffy or runny nose. Or there may be discolored mucus running from the nose. People with this condition might also have pain, swelling and tenderness around the eyes, cheeks, nose or forehead.

Steroid nasal sprays, allergy medicines and allergy shots might help.