The 4 Underlying Causes of Pink Eye

girl with pink eye

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  • Adenoviruses are a family of highly contagious viruses that target human organs lined with mucous membranes, which include your eyes, intestines, urinary tract and nervous system
  • In some cases, direct exposure of your eyes with harsh chemical products and foreign objects can cause pink eye

There are four main underlying causes of pink eye. The first two are contagious, while the remaining two are noncontagious. The information below provides an overview on how each of them causes pink eye.

Adenoviruses Cause Viral Conjunctivitis

Adenoviruses are a family of highly contagious viruses that target human organs lined with mucous membranes, which include your eyes, intestines, urinary tract and nervous system.1 They're known for causing various respiratory ailments, such as the common cold or the flu. They may also cause a urinary tract infection, or in this case, pink eye.2

Currently, there are more than 100 types of adenoviruses that have been documented,3 and 51 of them are known to cause an infection. The table below explains the connection of assorted diseases to the adenoviruses that cause them:4

Resulting Disease Adenovirus Types Responsible
Childhood febrile illness and pharyngoconjunctival fever 1 to 3, 5 and 7
Pneumonia and other acute respiratory illnesses 1 to 3, 5, 7 and 14
Pertussis-like illness 1 to 3, 5, 19 and 21
Conjunctivitis 1 to 4, 5, 7, 8, 19 and 21
Keratoconjunctivitis 3, 8, 9, 19 and 37
Upper respiratory illness and hepatitis 1 to 3, 5 and 7
Lower respiratory illness 3, 4, 7 and 21

Certain Bacteria Are Known to Cause Pink Eye, but Not as Often as Adenoviruses

Similar to adenoviruses, the second form of contagious pink eye is caused by certain strains of bacteria. The following shows the different bacteria strains, along with other diseases they’re known to cause:5

Staphylococcus aureus — Boils, cellulitis, food poisoning and toxic shock syndrome6

Streptococcus pneumoniae — Pneumonia, ear infections, sinus infections, meningitis and bacteremia7

Haemophilus influenzae — Cellulitis, epiglottitis, septic arthritis and hib pericarditis8

Chlamydia trachomatis —  Pelvic inflammatory disease, chlamydial pneumonia in newborns and urogenital infection in women9

Neisseria gonorrhoeae — Pelvic inflammatory disease and epididymitis10

Moraxella catarrhalis — Bronchitis, laryngitis, sinusitis and otitis media11

Allergies May Cause Conjunctivitis

It's possible for pink eye to manifest as a result of an allergic reaction. When an allergen enters your system, your body produces an antibody named immunoglobulin E (IgE), triggering your mast cells to produce inflammatory substances that cause pink eye.12

Though the condition is not contagious, the symptoms may persist if the allergens in your home are not eliminated. There’s also a possibility that you may experience seasonal conjunctivitis when allergy season arrives. Common allergens include:13

Dust mites

Pollen from trees and grass

Animal hair

Contact lenses

Man-Made Irritants May Cause Pink Eye

In some cases, direct exposure of your eyes to harsh chemical products and foreign objects can cause pink eye. These include common household items such as shampoos or chlorine from swimming pools. Other objects such as dust and smoke may also irritate your eyes.14 This condition is noncontagious and may last only for a day or two.15

Risk Factors for Getting Conjunctivitis

Several factors are involved in the case of developing pink eye. These include:16

Age — Newborns and elderly people are more susceptible to pink eye, possibly due to their weak immune systems.

Having a viral infection — If you're currently experiencing a respiratory infection such as the common cold or flu, you may have a chance of developing pink eye when saliva droplets from a sneeze or cough reach your eyes.

A condition that weakens your immune system — Ailments such as diabetes may weaken your immune system, leaving you susceptible to infection.

Taking medications — Certain medications, such as corticosteroids, may weaken your immune system, allowing viruses and bacteria to infect you easily.

Poor hygiene — Poor hygiene practices and carelessness in public places may leave you susceptible to a viral or bacterial infection.


Pink Eye: Introduction

What is Pink Eye

Pink Eye in Children

Pink Eye in Adults

Is Pink Eye Contagious?

Pink Eye Duration

Pink Eye Causes

Types of Pink Eye

Pink Eye Symptoms

Pink Eye Treatment

Pink Eye Prevention

Pink Eye Diet

Pink Eye FAQ

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