Redness and itchiness of the eyes are caused by the following: First, allergic conjunctivitis, in which particles such as smoke, pollen and dust suspended in the air form allergens that induce allergic reactions in the conjunctival tissue of the eye surface after contact. Second, allergic blepharitis, caused by the use of cosmetics around the eyes or the skin around the eyes to shampoos and cleansers. Third, blepharitis, a chronic infection of the lid margin caused by poor eye hygiene habits, associated with vitamin B2 deficiency. Fourth, bacterial conjunctivitis, most bacterial conjunctivitis does not cause itching in the eye, manifesting as redness of the eye, but if the infection is more severe, it can also stimulate the conjunctival tissue to form itching.