Similar to processes that occur with other types of allergic responses, the eye may overreact to a substance perceived as harmful even though it may not be. For example, dust that is harmless to most people can cause excessive production of tears and mucus in eyes of overly sensitive, allergic individuals. Eye allergies are often hereditary.
Allergies can trigger other problems, such as conjunctivitis (pink eye) and asthma. Most of the more than 22 million Americans who suffer from allergies also have allergic conjunctivitis, according to the American Academy of Ophthalmology.