Nasonex nasal spray can effectively treat and prevent the symptoms of allergic rhinitis. Nasonex effectively treats both seasonal and year-Round allergies. Nasonex contains the active ingredient mometasone furoate, which is a corticosteroid. Corticosteroids, such as mometasone have anti-Inflammatory properties. Nasonex nasal spray can also treat nasal polyps these are growths that develop at the nose alongside other allergy symptoms.