Allergic rhinitis occurs when the immune system overreacts to a harmless substance, called an allergen. The immune system is made up of special cells, called white blood cells, which fight infection. When an allergen is present in the body, white blood cells recognize the allergen, and release chemicals into the blood stream. These chemicals can cause inflammation of the inside lining to the nose, when it is exposed to an allergen.

Common allergens include:

• Animal dander
• Dust mites
• Fungi
• Grass
• House dust
• Household cleaners
• Indoor plants
• Insects
• Mold
• Pollen
• Rodents