Allergic rhinitis is an inflammation of the nasal airways that can occur when an environmental allergen, such as pollen or mold, is inhaled by an individual with a sensitized immune system. This type of allergic rhinitis is often referred to as hay fever and may be seasonal or perennial., , , , Since hay fever often involves an allergic reaction to pollen, the amount of pollen in the air will affect whether symptoms develop or not for many people. The types of pollen that cause hay fever vary.