Frequently , patients awake in the morning with a rude surprise - looking in the mirror to find a subconjunctival hemorrhage . For when we are sleeping and dreaming , we may rub our eyes with our hands while unconscious . The ' red eye ' appearance is caused by a patch of blood under the conjunctiva . Like any spontaneous bruise , a subconjunctival hemorrhage will fade within approximately two weeks . It requires no treatment .
Allergic eyes are generally more puffy than red .
Ocular itching is the hallmark complaint of allergies . Contact lens wearers may occasionally develop acute onset of red eyes associated with eye pain . It is associated with poor contact lens hygiene , over-wearing of contact lenses without allowing the eyes rest intervals , allergies to contact lens solutions or their preservatives , or the buildup of protein and bacterial deposits on the surface of the contact lenses . Sometimes blunt trauma to the eye may lead to bleeding inside the anterior chamber of the eye causing a ' red eye ' appearance . This potentially serious bleeding in the eye is termed ' hyphema ' .