I have horrible allergies
I have allergies that are mostly seasonal but really bad allergies to corn pollen which is unavoidable since I live in Iowa. 
I have terrible allergies too- especially to cats. What other kinds of allergies are there?
Food allergies and allergies to all types of pollen. That's why during certain seasons people develop hay fever especially during harvest.
What exactly causes allergies? 
It's a hypersensitivity of the immune system that is triggered by things in the environment. 
How are seasonal allergies different from food allergies?
Food allergies happen anytime you touch or ingest a certain food. Seasonal allergies happen during peak times of the year when pollen or other plants particles are in the air. 
What are cat allergies considered? 
Cat allergies are considered an environmental allergy due to the cats being in the environment. Pet allergies are usually caused by the pet dander.