An allergy is when the body's immune system reacts to something (called an allergen) that is normally harmless. When an allergen comes in contact with your eye, certain cells within the eye (called mast cells) release histamine and other substances to fight off the allergen. This reaction causes your eyes to become red, itchy and watery.
Many eye allergies are caused by the body’s response to allergens in the air — both indoors and out — such as dust, pet dander, mold, or smoke. Some of the most common airborne allergens include pollen from grass, trees and ragweed, contributing to seasonal allergies.
Allergic reactions to perfume, cosmetics or drugs can also cause the eyes to have an allergic response. Some people may be allergic to the preservative chemicals in lubricating eyedrops. They should use preservative-free drops instead.
Sometimes, the eyes can react to other allergens that don't necessarily come in direct contact with the eye, such as specific types of food or insect bites or stings.
Some people can inherit eye allergies from their parents. You're more likely to have allergies if both of your parents have them than if only one does.
Next Page: Eye Allergy Diagnosis