If your eyes are itchy, watery, red and swollen, if your nose is running and you can't stop sneezing, you may be suffering from hay fever, a seasonal allergy caused by contact with airborne allergens.

In the spring, allergies are commonly caused by pollen from trees, weeds and grass. Indoor allergens such as pet dander or hair, dust or mold can also cause allergies year round.

Allergy symptoms occur as a response to an allergen, when the body overreacts by releasing histamines. Histamines are chemicals that the body releases to defend itself against allergens. Eye allergy symptoms are caused by the release of histamine by mast cells in the eye, which causes blood vessels in the eye to swell and symptoms such as tearing, itching and redness. Histamine irritates nerve endings, causing red and swollen eyes and tears are released by the tear ducts.