Red eyes are pretty common and often clear on their own without treatment. The anomaly occurs when the tiny blood vessels in the eye get enlarged or burst because of irritation or infection. It may also be a sign of dryness or allergies. However, redness associated with an injury, glaucoma, corneal cuts, scratches, or sores might require medical attention. See an eye doctor if your eye hurts, if you have trouble seeing or if the symptom does not improve within a couple of days.