Eye allergies occur when the eyes become overly sensitive to something in the immediate environment. This oversensitivity causes the immune system to respond to what is, under most circumstances, a harmless substance as though it were a danger to your health.

The part of the eye that is most likely to experience an allergic response is the clear tissue that lines the interior of the eyelid and the surface of the eyeball, keeping it moist. This tissue is known medically as the conjunctiva, which is why eye allergies are also called allergic conjunctivitis. Symptoms of eye allergies include redness, itching, burning, swelling, tearing, and light sensitivity. 

A variety of indoor and outdoor allergens can trigger the eye’s immune reaction. These include pet dander, dust mites, mold spores, and pollen from trees, grasses, and weeds. A related category of irritants includes dust, tobacco smoke, exhaust fumes, and perfume, which can produce a similar response but are not technically allergens.