Seeing Red: Understanding the Pathology of Pink Eye

Your eyes might itch, swell, and water during allergy season, but one symptom can really cause heads to turn. Conjunctivitis, also known as pink eye, is a generic term that describes inflammation of an ocular membrane and subsequent reddening of the eye.1 However, this reaction isn’t limited to allergy season. Conjunctivitis comes in four categories: chemical, allergic, viral, and bacterial.1–3 This article will provide an overview of this health condition and explain its types, causes, symptoms, treatment, and prevention. 

Three Shades of Pink Eye

Conjunctivitis occurs when an irritant causes the transparent membrane of your eye to become inflamed. During these episodes, the small blood vessels lining this membrane, called conjunctiva, swell and redden, which makes them more visible.1,3,4 This reaction is what causes the trademark pink of conjunctivitis. This inflammation can have several causes, which inform the four types of pink eye.

Chemical and allergic conjunctivitis. Chemical and allergic conjunctivitis, the only types that are not contagious, are caused by reactions to specific irritants or environmental triggers, such as pollen, animal dander, chlorine, smoke, dust, and certain fumes.1,5–7 Its symptoms are those typically associated with seasonal allergies: itching, watering, and redness. This type of pink eye is most common among those who already have seasonal allergies, but all people are susceptible to these kinds of reactions.

Viral conjunctivitis. When most people think of conjunctivitis, they think of viral pink eye. This is the most common type, accounting for about 80 percent of acute conjunctivitis cases.7 It is often linked to epidemic keratoconjunctivitis, a highly contagious eye infection caused by a family of viruses called adenoviruses, but cases can also be caused by other infections, including viruses that cause the common cold.5,7–9 Burning, water discharge, and redness are the most common symptoms.

Bacterial conjunctivitis. This type is caused by bacteria, usually staphylococcal or streptococcal bacteria, infecting the eye.1 Like its viral counterpart, bacterial conjunctivitis is highly contagious and can be spread when shared infected items come into contact with the eye.1,4,10 It typically causes soreness, inflammation, and thick green or yellow discharge in the eye.10–12

As mentioned above, specific symptoms can be associated with a certain type of pink eye.1,13 More general symptoms, including redness, swelling, increased tear production, sensitivity to light, irritation, and the crusting of eyelids and eyelashes, can be present in all four types of conjunctivitis. Anyone is susceptible to pink eye. While these cases do not always require a visit to your healthcare provider, symptoms that are severe or do not improve within a week are signs that further intervention is needed.3,5 However, newborns with symptoms of pink eye should see a doctor right away.8,11,12

Conjunctivitis Treatment

Conjunctivitis is diagnosed through a comprehensive eye examination and supplemental testing, which involves taking culture samples of conjunctival tissue.4,11 No matter which type is present, pink eye treatment has three main goals, according to the American Optometric Association; they are increasing patient comfort, reducing or lessening the course of the infection or inflammation, and preventing the spread of the infection in cases of contagious forms of conjunctivitis.11 The method of treatment often depends on the type of pink eye present.1,5,10

Non-contagious cases of pink eye can begin with removing the triggers when possible. This might involve stepping into an area sealed from pollen or using water to flush out an eye that has been affected by some type of irritant. Once these triggers have been removed, mild cases can be soothed with cool compresses, artificial tears, or antihistamines.6,8

Infectious cases of pink eye often require more targeted treatment from a doctor. These modalities often include medication, eye drops, or ointments.4,11,13 Those with bacterial conjunctivitis are able to take a more proactive approach using antibiotics. Symptoms often improve within 3 to 4 days after starting this regimen, but patients must complete the entire course of antibiotics to prevent recurring infections. Treatment for viral pink eye is much slower. Because viruses cannot be treated with antibiotics, patients are forced to let the infection run its course, which may take up to three weeks to finally subside.5 In severe cases, a doctor may prescribe topical steroid drops to reduce inflammation and discomfort.14 

Preventing Pink Eye

Infectious cases of pink eye are notoriously contagious. Viral cases can be spread to others before an infected person has symptoms, while bacterial conjunctivitis is contagious once symptoms start and up to 48 hours after starting antibiotics.8,15 Like other viral and bacterial infections, viral and bacterial conjunctivitis are transmitted by touching the affected eye and then touching an item or surface, such as a light switch or keyboard.5,6,17 There’s a reason pink eye spreads so quickly in schools! That’s why protecting yourself and others from these infections is so crucial. The Centers for Disease Control and Prevention recommends the following steps to reduce your risk of contracting pink eye:12

Thoroughly wash your hands with soap and water, especially during an outbreak of pink eye or after being in contact with someone who has infectious conjunctivitis.

While you should avoid touching your eyes as a general rule, abstaining from this habit is especially important in preventing conjunctivitis. Touching or rubbing an infected eye can worsen the condition or spread it to your other eye. This also includes sharing personal items that come into contact with your eyes, such as makeup and cosmetic brushes, eye drops, towels, pillowcases, eyeglasses, and contact lenses, solutions, and containers.

To prevent further contamination of contacts and related products, stop wearing contact lenses until your healthcare provider gives the okay. Similarly, always clean, store, and replace these items as instructed by your doctor.

Before returning to the workplace or classroom, make sure your symptoms are entirely gone. If you have a bacterial infection, ask your doctor if you can return after taking an antibiotic for 24 hours.2,8,15

Bottom Line

Whether cases are caused by irritants, injuries, environmental triggers, or infections, pink eye can be debilitating. The symptoms of conjunctivitis range from uncomfortable to painful and can intensely affect quality of life. Luckily, most cases are easily treatable by healthcare providers if they do not resolve on their own. Because infectious cases are so contagious, all people are susceptible to this disease. As is the case with many other illnesses, an ounce of prevention is worth a pound of cure. Hand washing, abstaining from touching infected eyes, basic hygiene practices, and abiding by your healthcare provider’s instructions for treatment are all key strategies for protecting yourself from and preventing the spread of pink eye in your community.

  1. Azari AA, Arabi A. Conjunctivitis: a systematic review. J Ophthalmic Vis Res. 2020;15(3):372–395. 
  2. Mayo Clinic Staff. Pink eye (conjunctivitis). Mayo Clinic. 19 Mar 2024. Accessed 20 Mar 2024.
  3. National Eye Institute. At a glance: pink eye. 15 Nov 2023. Accessed 10 Mar 2024.
  4. Hashmi MF, Gurnani B, Benson S. Conjunctivitis. In: StatPearls. StatPearls Publishing; 2024.
  5. Boyd K. Conjunctivitis: what is pink eye? American Academy of Ophthalmology. 15 April 2023. Accessed 17 Mar 2024.
  6. Villegas BV, Benitez-Del-Castillo JM. Current knowledge in allergic conjunctivitis. Turk J Ophthalmol. 2021;51(1):45–54.
  7. Muto T, Imaizumi S, Kamoi K. Viral conjunctivitis. Viruses. 2023;15(3):676. 
  8. Bedinghaus T. What is conjunctivitis? Verywell Health.13 Mar 2022. Accessed 17 Mar 2024.
  9. Bedinghaus T. An overview of epidemic keratoconjunctivitis. Verywell Health. 30 Sep 2021. Accessed 17 Mar 2024.
  10. Mahoney MJ, Bekibele R, Notermann SL, et al. Pediatric conjunctivitis: a review of clinical manifestations, diagnosis, and management. Children (Basel). 2023;10(5):808.
  11. American Optometric Association.Conjunctivitis (pink eye). Accessed 25 Mar 2024.
  12. Centers for Disease Control and Prevention. Conjunctivitis (pink eye). 12 Nov 2021. Accessed 25 Mar 2024.
  13. Azari AA, Barney NP. Conjunctivitis: a systematic review of diagnosis and treatment. JAMA. 2013;310(16):1721–1729.
  14. Holland EJ, Fingeret M, Mah FS. Use of topical steroids in conjunctivitis: a review of the evidence. Cornea. 2019;38(8):1062–1067.
  15. Cleveland Clinic. Pink eye (conjunctivitis). 22 Aug 2022. Accessed 26 Mar 2024.
  16. Bever L. Pinkeye cases rise in allergy season. It might be a Covid symptom, too. Washington Post. 21 Apr 2023. Accessed 26 Mar 2024.   

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