Redness of eyes is due to the swelling of microvessel on the surface of the eye. There are several reasons why the eyes will turn red. One is because the eyes are in direct contact with sensitive or irritating substances, such as smoke, perfume, chemicals, alcohol, etc. The second reason is because of dryness of the eyes. Prolonged exposure to electronic products, insufficient sleep, insufficient tear secretion, excessive use of eyes, prolonged duration in air-conditioning room or wearing contact lenses for too long duration can cause eye dryness. The third cause may be due to bacterial infections, and the fourth cause is due to some serious eye diseases such as glaucoma.