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Causes
By Mayo Clinic staffDuring a process called sensitization, your immune system mistakenly identifies a harmless airborne substance as something harmful. Your immune system then starts producing allergy-causing antibodies. 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.
Hay fever can be triggered by either seasonal or year-round (perennial) allergens. Many people have allergy symptoms all year long, but their symptoms get worse during certain times of the year.
Seasonal hay fever triggers include:
- Tree pollen, common in the spring
- Grass pollen, common in the late spring and summer
- Weed 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
- Cockroaches
- 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.
