When blood vessels in and around the eye expand because of some form of irritation, the eye and area around it appear red. “Red eye” is the general term for any condition that causes this redness. Red eye can be caused by:
Eye infections
Dry eyes
Eye injuries
Foreign objects in the eye
Pink eye (also called conjunctivitis) is a common cause of red eye. While red eye is a very general, non-clinical term, pink eye is the medical term for inflammation of the lining covering the eyeball and eyelid. Pink eye can be caused by:
A virus – The same virus that causes many colds and cases of flu can also cause pink eye. This form is contagious and the most common type of pink eye.
Bacteria – Bacterial infections can also result in pink eye. Bacterial pink eye is contagious and may cause mucus discharge from one or both eyes.
Allergies – The same substances that cause allergic reactions, like pollen or smoke, can cause non-contagious pink eye.