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Causes

By Mayo Clinic staff

During a process called sensitization, your immune system mistakenly identifies a harmless airborne substance as something harmful. Your immune system then starts producing antibodies to this harmless substance. The next time you come in contact with the substance, these antibodies recognize it and signal your immune system to release chemicals, such as histamine, into your bloodstream. These immune system chemicals cause a reaction that leads to the irritating signs and symptoms of hay fever.

Seasonal hay fever triggers include:

  • Tree pollen, common in the spring
  • Grass pollen, common in the late spring and summer
  • Ragweed pollen, common in the fall
  • Spores from fungi and molds, which can be worse during warm-weather months

Year-round hay fever triggers include:

  • Dust mites or cockroaches
  • Dander (dried skin flakes and saliva) from pets, such as cats, dogs or birds
  • Spores from indoor and outdoor fungi and molds

Hay fever doesn't mean you're allergic to hay. Despite its name, hay fever is almost never triggered by hay, and it doesn't cause a fever.

Risk factors Symptoms
References
  1. Allergic rhinitis (hay fever). American Academy of Allergy, Asthma and Immunology. http://www.acaai.org/allergist/allergies/types/rhinitis/Pages/default.aspx. Accessed March 30, 2012.
  2. McPhee SJ, et al. Current Medical Diagnosis & Treatment 2012. 51st ed. New York, N.Y.: The McGraw-Hill Companies; 2012. http://www.accessmedicine.com/content.aspx?aID=2356. Accessed April 1, 2012.
  3. Ferri FF. Ferri's Clinical Advisor 2012:5 Books in 1. Philadelphia, Pa.: Mosby Elsevier; 2012. http://www.mdconsult.com/books/about.do?about=true&eid=4-u1.0-B978-0-323-05611-3..C2009-0-38601-8--TOP&isbn=978-0-323-05611-3&uniqId=291436269-101. Accessed March 31, 2012.
  4. Longo DL, et al. Harrison's Online. 18th ed. New York, N.Y.: The McGraw-Hill Companies; 2012. http://www.accessmedicine.com/content.aspx?aID=9136197. Accessed April 1, 2012.
  5. Fact sheet: Allergic rhinitis (hay fever). American Academy of Otolaryngology — Head and Neck Surgery. http://www.entnet.org/HealthInformation/allergicRhinitis.cfm. Accessed March 30, 2012.
  6. Greiner AN, et al. Allergic rhinitis. The Lancet. 2011;378:2112.
  7. Allergies and hay fever. American Academy of Otolaryngology — Head and Neck Surgery. http://www.entnet.org/HealthInformation/allergiesHayFever.cfm. Accessed March 30, 2012.
  8. Rhinitis and sinusitis. Asthma and Allergy Foundation of America. http://www.aafa.org/display.cfm?id=9&sub=18&cont=239. Accessed March 30, 2012.
  9. Montelukast sodium. Micromedex Healthcare Series. http://www.micromedex.com. Accessed April 2, 2012.
  10. Naegleria FAQs. Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/naegleria/faqs.html. Accessed Dec. 30, 2011.
  11. Man L. Complementary and alternative medicine for allergic rhinitis. Current Opinion in Otolaryngology and Head and Neck Surgery. 2009;17:226.
  12. Allergic rhinitis (hayfever). Natural Medicines Comprehensive Database. http://www.naturaldatabase.com. Accessed April 2, 2012.
  13. Li JT (expert opinion). Mayo Clinic, Rochester, Minn. April 3, 2012.
DS00174 July 17, 2012

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