An unusual reaction or sensitivity to an allergen, a substance which doesn't bother most people. Hay fever, of course, is not caused by Hay and doesn't produce a fever. Avoid the allergens that trigger your symptoms. Consult your pharmacist about allergy relief medication which can be purchased over the counter. Spend as much time indoors with air conditioning as possible.
Fans spread pollens.
Keep car vents and windows shut if you have allergies. Wear a paper filter mask when cutting the grass. Consider an electronic filter for your home. Choose an ocean vacation over a trip to the mountains. Stay indoors when it goes over 80.