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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
 

The 4 Underlying Causes of Pink Eye

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There are four main underlying causes of pink eye. The first two are contagious, while the remaining two are non-contagious. 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:5,6

Staphylococcus aureus: Boils, cellulitis, food poisoning and toxic shock syndrome7

Streptococcus pneumoniae: Pneumonia, ear infections, sinus infections, meningitis and bacteremia8

Haemophilus influenzae: Cellulitis, epiglottitis, septic arthritis and hib pericarditis9

Chlamydia trachomatis: Pelvic inflammatory disease, chlamydial pneumonia in newborns and urogenital infection in women10

Neisseria gonorrhoeae: Pelvic inflammatory disease and epididymitis11

Moraxella catarrhalis: Bronchitis, laryngitis, sinusitis and otitis media12

Allergies May Cause Conjunctivitis

It's possible for pink eye to manifest as a form of 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.13 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:14

Household dust

Pollen from trees and grass

Mold spores

Animal dander

Scents from household detergents and perfume

Man-Made Irritants May Cause Pink Eye

In some cases, direct exposure of your eyes with 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.15 This condition is non-contagious and may last only for a day or two.16

Risk Factors for Getting Conjunctivitis

Several factors are involved in the case of developing pink eye. These include:17

Your 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.

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