Allergic rhinitis (hay fever) is an IgE-mediated immune reaction to airborne allergens. It affects between 1 in 6 and 1 in 10 people, with 70% of cases occurring before age 30. Symptoms resemble those of viral rhinitis but persist and show seasonal variation. This most common form of allergy involves the entire respiratory system - nasal cavity, mouth, throat, bronchi and lungs - and the eyes. There is an inherited tendency, with a child having a 50% chance of developing such allergy if one parent is allergic, and a 75% chance if both parents are allergic.