A seasonal allergy is usually defined as an allergic reaction to a trigger that is typically only present for parts of the year, such as spring or fall. This type of allergy means the sufferer is allergic to pollen from trees, weeds, and grasses. In contrast, perennial allergies are present all year round and occur in reaction to allergens such as pet dander and house dust mite. In the case of molds, they can cause either seasonal or perennial allergy.

The main reason for a runny nose and a fever that accompanies a seasonal allergy is a histamine overdrive. Histamine fights alien invaders such as allergens but overproduction can backfire causing sneezing, itching and watery eyes. 

Foods that contain histamine in them can also cause an allergy with symptoms manifesting as sneezing, coughing, headaches and itching. As such these foods are to be avoided if you are prone to seasonal allergy attacks.