Causes and Risk Factors of Pink Eye

pink eye causes
Illustration by Joshua Seong. © Verywell, 2018.

Conjunctivitis, more commonly known as pink eye, affects as many as six million people each year in the United States. It is important to understand the different causes and risk factors of conjunctivitis in order to know how to properly manage your symptoms and to prevent recurrence.

Overall, conjunctivitis falls into two main categories: infectious and non-infectious.

Infectious conjunctivitis is caused by bacteria, viruses, or fungi while non-infectious causes include allergies, chemical irritants, and foreign bodies.

Causes of Viral Conjunctivitis

Viruses account for 80 percent of all cases of conjunctivitis with up to 90 percent of those cases caused by adenovirus and five percent by herpes simplex virus. The most common symptoms are eye redness and watery discharge.

Other common viruses include:

Treatment is rarely needed for these infections as they usually resolve on their own. However, there are two important exceptions that require referral to an ophthalmologist.

Herpes infections

Not only can herpes infections like herpes simplex and varicella-zoster inflame the conjunctiva but they can sometimes cause corneal ulcers or scarring of the cornea that could affect your vision.

There are tests your healthcare provider can perform to find out if you have a herpes infection.

Epidemic keratoconjunctivitis

One rare form of viral conjunctivitis, epidemic keratoconjunctivitis (EKC), is caused by specific serotypes of adenovirus. EKC inflames both the cornea and the conjunctiva, potentially causing changes to your vision.

In addition to watery discharge, you may feel like there is a foreign body in your eye.

Causes of Bacterial Conjunctivitis

Bacterial causes of conjunctivitis are far less common. Ocular discharge is typically thick and purulent as opposed to the watery discharge often seen with viral infections. Bacterial conjunctivitis should be treated with appropriate antibiotics when possible to decrease the spread of infection.

Common Causes

  • Staphylococcus aureus
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Moraxella catarrhalis

S. aureus is the most common bacteria found in adults while children are more likely to be infected by the other bacteria listed. In most cases, these bacteria are easily treated.

The one exception is the methicillin-resistant S. aureus (MRSA). MRSA infection will require an ophthalmology consultation and treatment with specific antibiotics.

Rare Causes

There are two aggressive bacterial infections that warrant further attention. While they are not common, they could increase the risk of vision loss. A formal ophthalmology evaluation is advised.

Chlamydia trachomatis and Neisseria gonorrhoeae are the bacteria responsible for the sexually-transmitted infections you know more commonly as chlamydia and gonorrhea.

While we do not often think of these sorts of infections as getting into the eyes, it happens. For example, someone can rub their eyes after touching infected body fluids or secretions.

The population at greatest risk for these infections are newborns. If the mother is infected at the time of delivery, transmission of the bacteria happens as the baby exits the birth canal. Because chlamydia and gonorrhea do not always cause symptoms, the mother may or may not know she is infected. It is for this reason that the standard of care at delivery is to treat all newborns with antibiotic ointment.

Allergic Conjunctivitis

People who have seasonal allergies, asthma, and eczema are at increased risk of developing allergic conjunctivitis.

What distinguishes allergic conjunctivitis from the infectious types is the itching. Like viral conjunctivitis, ocular discharge tends to be watery.

Seasonal allergies account for 90 percent of all allergic conjunctivitis cases. The remaining cases may be caused by other allergic exposures or chronic allergies. In very rare cases, the inflammation caused by the allergic response extends to the cornea, leading to atopic keratoconjunctivitis (AKC). As with any keratitis, there is an increased risk of vision impairment if AKC is left untreated.

Other Common Causes

Other forms of conjunctivitis are usually short-lived and may be caused by the following.

Chemical Exposures

If a chemical gets into your eye, it can cause irritation and redness. Chlorinated pool water is a common example.

It is also possible that a toxic chemical gets splashed into your eye. Eye irrigation may remove the offending agent but could also cause eye redness in and of itself. Redness after irrigation usually improves within a day. 

Foreign Bodies

A foreign body in the eye, even an eyelash, can trigger eye redness and inflammation for up to a day after it is expelled. Eye irrigation to remove that foreign body can add to that irritation.

More concerning is when a foreign body exposure is more chronic in nature. This is where ​giant papillary conjunctivitis (GPC) comes into play. GPC occurs when the eyelid rubs repeatedly against a foreign body like a contact lens or a surgical stitch. An immune reaction is triggered that leads to local inflammation.

Not only will people with GPC get itchy watery eyes, they often describe a gritty sensation. The eyelid also thickens and forms small bumps on the underside of the eyelid that help to establish the diagnosis.

GPC is more likely to occur if debris has collected on your contact lens. It is ten times more common in users of soft contact lenses than hard contacts. Still, it is not very common, affecting only one to five percent of soft contact users.

Lifestyle Factors

You may not be able to control whether someone near you gets conjunctivitis but you can take steps to decrease the risks to yourself.

Contact Lenses

Wearing contact lenses could increase your risk for conjunctivitis in a number of ways. The contact lens cleaning solution could become infected with bacteria or the solution itself could be chemically irritating to the eye. The contact lens itself may not fit properly or deposits may build up on the lenses after long-term use or with improper cleaning.

If you use contact lenses, take care to clean them properly and to see an eye doctor if you have discomfort with use.

Dry Eyes

People with dry eye syndrome are more prone to develop pink eye. You may consider using hydrating eye drops or seeking an evaluation with an eye doctor to see if other treatments are indicated.

Hygiene

Poor hygiene makes it more likely that you could spread infection from one eye to the other or it can spread from one person to another. Frequent handwashing is key. Also avoid touching or rubbing your eyes and sharing anything that could come into contact with your eyes, i.e., contact lenses, eye makeup, eyeglasses, pillows, or towels.

Sources:

Azari AA, Barney NP. Conjunctivitis: A Systematic Review of Diagnosis and Treatment. JAMA. 2013 Oct 23; 310(16): 1721–1729. doi: 10.1001/jama.2013.280318.

Conjunctivitis (Pink Eye). Centers for Disease Control and Prevention. https://www.cdc.gov/conjunctivitis/clinical.html. Updated October 16, 2017.

Jacobs DS. Conjunctivitis. In: Sullivan DJ (Ed), UpToDate (Internet), Waltham, MA. Updated February 2018.

O'Callaghan RJ. The Pathogenesis of Staphylococcus aureus Eye Infections. Pathogens. 2018 Jan 10;7(1). pii: E9. doi: 10.3390/pathogens7010009.

Suchecki JK, Donshik P, Ehlers WH. Contact Lens Complications. Ophthalmol Clin of North Am. 2003 Sep 01, 16(3):471-484. doi: 10.1016/S0896-1549(03)00056-7.