Conjunctivitis. Artwork of an eyedrop being added to an eye suffering from conjunctivitis. This is an inflammation of the conjunctiva, the transparent membrane that covers the eye and lines the eyelids. It causes itching, irritation, redness (bloodshot) and a discharge from the eye. The most common causes are infection and allergy. Most infections are caused by bacteria or viruses spread by hand-to-eye contact. Allergic conjunctivitis can be provoked by many substances including cosmetics, contact lens cleaning solutions and pollen (hay fever). Antibiotic or antihistamine eye drops can be used to treat infections and allergies respectively.