It's not usually produced by hay, however, and there is no fever. The trees are blooming and at the end of May or beginning of June the grass will pollinate. Allergy is an overreaction to environmental pollens, mites in house dust, animal dander, molds, and rarely foods. Allergic fellow travelers are eczema, hay fever, and asthma. The allergic tendency often runs in families.
Some families have more asthma than others.
Unusually and persistent levels of antibody to just the things you are allergic to are the cause of these of possible allergies. Non-allergic people make the same antibodies, but not as much and not as persistently. People who overuse nose drops can get rebound swelling. Initially there is help with considerable worsening hours later. It will take two weeks of abstinence to cure.