Hay Fever Overview
Hay fever, also called allergic rhinitis, upper respiratory tract allergies, and allergic conjunctivitis, is a common condition. Hay fever is caused by an abnormal immune system response to substances (called allergens) that are produced seasonally in nature and are carried through the air.
Hay fever allergy symptoms—watery, itchy eyes, congestion, allergic cough, sneezing, and runny nose—occur when the immune system overreacts to inhaled allergens and produces an antibody called immunoglobulin E (IgE). This antibody binds to cells in the body (called mast cells) and causes the release of histamine (a substance that dilates blood vessels) and other chemicals.
The most common outdoor allergens are airborne mold spores and pollen from trees, grasses, and weeds. Common indoor allergens include dust mites, animal proteins (e.g., dander, saliva), mold spores, and cockroach secretions/debris (e.g., fecal matter, saliva).
Incidence and Prevalence of Hay Fever
According to the American Academy of Allergy, Asthma & Immunology (AAAAI), more than 35 million people in the United States (15–20 percent of the population) are affected by hay fever allergies. The Asthma and Allergy Foundation of America reports that hay fever is the fifth leading chronic condition in the United States and the third most common chronic condition in children and adolescents younger than age 18. Outdoor and seasonal allergies account for more than half of all allergy-related medical appointments.