Allergic conjunctivitis is inflammation of the conjunctiva (the membrane covering the white part of the eye) ue to allergy. Although allergens differ between patients, the most common cause is hay fever. Symptoms consist of redness (mainly due to vasodilation of the peripheral small blood vessels), oedema of the conjunctiva, itching and increased lacrimation (production of tears). If this is combined with rhinitis, the condition is termed allergic rhinoconjunctivitis.