What causes red eye?

In general, anything that irritates or inflames the white part of your eye can cause red eye. The redness you see is usually caused by an increase in the size of small vessels in your eye, which allows more blood into the white portion of your eye, making it appear red. Sometimes a bright red patch, called a subconjunctival hemorrhage, appears in the white of your eye as a result of the breakage of small, superficial blood vessels.

Physical irritation from chemicals in the environment or the home or from prolonged wearing of contact lenses frequently causes red eye. Allergies, blepharitis (inflammation of the eyelid margin), and conjunctivitis (inflammation of the eye surface) are other very common causes of red eye. Trauma in the eye area, whether blunt or penetrating, is a more worrisome reason for red eye. Acute angle-closure glaucoma (sudden increase of the pressure in your eye) as well as uveitis and iritis (inflammation of structures of the eye) are vision-threatening causes of red eye, but fortunately, they are not common.

Common causes of red eye

Red eye symptoms may be caused by several common conditions including:

  • Blepharitis (inflammation of the eyelid margin)
  • Common cold (viral respiratory infection)
  • Conjunctivitis (inflammation of the eye surface)
  • Crying
  • Fatigue
  • Hay fever or allergic reaction from animal dander, dust, cosmetics or pollen
  • Irritation from chemicals, environmental factors, or contact lenses
  • Lack of sleep
  • Local allergic reactions to makeup or personal care products (contact dermatitis)
  • Medicamentosa (eye develops sensitivity to eyedrops after long-term use)
  • Stye or hordeolum (localized bacterial infection of an oil gland or eyelash follicle in the eyelid margin)

Serious causes of red eye

Red eye can also be caused by more serious conditions including:

  • Acute glaucoma (sudden increase of pressure in the eye)
  • Corneal ulcer
  • Endophthalmitis (infection inside the eyeball)
  • Herpes infections
  • Orbital cellulitis (invasive infection of the soft tissues around the eye)
  • Periorbital cellulitis (infection of the eyelids or other soft tissue around the eyes)
  • Uveitis and iritis (inflammation of structures of the eye)
  • Trauma

Questions for diagnosing the cause of red eye

To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your red eye including:

  • When did you first notice your red eye?
  • Are you taking any medications?
  • Do you have any allergies?
  • Has anything hit you in the eye or flown into your eye?
  • Have you been around anyone with an eye infection recently?
  • Have you had a similar condition before?
  • Have you had recent eye surgery?
  • Do you have red eye in one or both of your eyes?
  • What other symptoms do you have?

What are the potential complications of red eye?

Red eye is usually the result of mild conditions that do not cause permanent damage to the eye. In rare cases, red eye is caused by a serious condition, including glaucoma or trauma, that, left untreated, can lead to permanent damage to the eye. Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:

  • Chronic eye pain or discomfort
  • Loss of the eye and orbit (bone surrounding the eye)
  • Loss of vision and blindness
  • Scarring of the eye
  • Spread of infection


  1. Eye burning - itching and discharge. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/003034.htm.
  2. Eye redness. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/003031.htm
  3. Kahan S, Miller R, Smith EG (Eds.). In A Page Signs & Symptoms, 2d ed. Philadelphia: Lippincott, Williams & Williams, 2009.

What is red eye?

Red eye is the result of changes in the blood vessels in your eye that make your eye look red or bloodshot; it may occur in one or both eyes. Red eye is usually caused by irritation, infection or trauma. Even everyday causes, such as coughing, sneezing, crying, and lack of sleep, can lead to redness in your eye. Red eye is often accompanied by other eye symptoms, including burning, itching, sor... Read more about red eyeintroduction


What other symptoms might occur with red eye?

Depending on the cause of your red eye, other parts of your body may also be affected. A variety of symptoms commonly occur along with red eye.

Common symptoms that may occur along with red eye

Red eye may accompany other common symptoms including:

Medical Reviewer: William C. Lloyd III, MD, FACS Last Annual Review Date: Sep 6, 2013 Copyright: © Copyright 2014 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

This Article is Filed Under: Eyes and Vision

Popular Eyes and Vision Slide Show