Conjunctivitis is an inflammation of the mucosal membrane of the eye (the conjunctiva). The ease with which this membrane is exposed to certain allergens and its anatomical and physiological characteristics cause the conjunctiva to be the part of the eye most affected by allergic reactions. Allergens can reach the membrane through the air (aerotransported allergens), by contact (hands, application of drugs) or through the bloodstream. In this context, tears exert a cleansing action by removing allergens and inflammatory mediators. The fundamental discomfort caused by allergic conjunctivitis is itching, which serves to differentiate the condition from bacterial conjunctivitis—which is characterised by morning bleariness of the eyes.