Hay fever, also known as allergic rhinitis, is a type of allergy to pollen, dust, or pet dander. Mold can also sometimes trigger the symptoms of hay fever. There are two basic types of hay fever, seasonal and perennial. Seasonal, as the name implies affects people most during the changes of the seasons, usually from spring to summer and summer to fall. Perennial hay fever affects a person all year long. Sometimes, people can experience both types of hay fever at once, with the symptoms becoming worse around the changes of the seasons.