Ocular allergies, called allergic conjunctivitis, are a common condition which happens when the eyes react to something that irritates them (an allergen). The eyes secrete a substance called histamine to fight the allergen. As a result, the eyelids become red, swollen and itching. Unlike bacterial or viral conjunctivitis, allergic conjunctivitis cannot be spread from person to person.
People who suffer from allergic conjunctivitis often (but not always) have pollen allergies in spring, and also experience itching, blocked nose and sneezing. The condition is usually temporary, but acute and connected to seasonal allergies. In other cases, allergic conjunctivitis can also develop from exposure to other allergens such as pets, dust, smoke, perfumes or even foods.