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4 Common Causes of Conjunctivitis – Bard Optical

4 Common Causes of Conjunctivitis

Hands washing with soap to avoid conjunctivitis

Conjunctivitis is the most common eye disease.

Fortunately, it is also one of the least serious. Most cases resolve on their own within a week. The exact length can depend on the cause of conjunctivitis: bacteria, viruses, allergies, or physical irritants.

Conjunctivitis is commonly known as pink eye.

The conjunctiva is a thin membrane that covers the inside of the eyelid, as well as the outside of the eyeball underneath the eyelid. The slippery membrane helps the eyelid move smoothly over the sclera or white surface of the eyeball. This layer provides the immune protection of a physical barrier to the rest of the eye. The conjunctiva also helps the lacrimal gland produce tears, as well as a small amount of mucus.

1. Bacterial conjunctivitis occurs when the conjunctiva becomes inflamed as a result of infection.

The first signs are often redness, swelling, sensitivity, itching, or pain. Watery eyes and redness occur as the many small blood vessels in the conjunctiva produce discharge. Overnight, the discharge can build up to a point that the eyelids are stuck shut by a yellow-whitish mucus that can harden into a crust.

By far the most common causes of conjunctivitis are bacterial and viral. Their symptoms are also very similar. Usually, it is not necessary to test which germ is the cause. According to the National Library of Medicine, “Doctors generally … prescribe antibiotic eye drops or creams just in case, even though these medications are only effective against bacteria.”

While bacterial and viral conjunctivitis can be difficult to tell apart, the bacterial type is more common among children than adults, making it a leading cause of absences from school or daycare. Both types are highly contagious, but the bacterial type is more likely to occur in the winter months between December and April.


2. Viral conjunctivitis can happen during a cold, flu, or respiratory infection.

With viral infections, the discharge from the eye tends to be more watery than the thick yellow pus associated with bacterial infections. The highly contagious infection typically starts in one eye but is easy to spread to the other eye within a day or two.

Viral infections usually take longer to clear than bacterial, typically resolving in a couple of weeks to a month. Because the inflammation is caused by a virus and not bacteria, there is no medicine that will cure the infection. However, being vaccinated against many common viruses can lessen the risk. Adenovirus is a very typical viral agent in cases. Vaccines against the following diseases are associated with a lower risk of conjunctivitis:

  • Rubella
  • Measles
  • Chickenpox
  • Shingles
  • Pneumococcal
  • Flu – Haemophilus influenza type b (Hib)

3. Allergies are also a common cause of conjunctivitis. 

As with most causes of allergies, symptoms will improve when the source of allergy is removed from a person’s environment. This type is not contagious because it is an autoimmune response. Eye drops with antihistamines or vasoconstrictors can help improve symptoms. Working with a doctor may be necessary to determine the particular causes and the best treatment options to deal with allergic conjunctivitis.


4. Eye irritants are less common as a cause of conjunctivitis than bacteria, viruses, or allergies.

This kind of inflammation may require further investigation by an ophthalmologist. A physical or chemical contaminant that has made its way into the eye will also produce the inflammation and redness characteristic of conjunctivitis. The Centers for Disease Control lists these possible sources of physical and chemical irritation:

  • chemical substances exposure
  • foreign bodies in the eye (like a loose eyelash)
  • indoor and outdoor air pollution caused by chemical vapors, fumes, smoke, or dust
  • fungi
  • amoeba and parasites
  • improper contact lens wear

Wearing contact lenses longer than indicated or not cleaning them properly can introduce contaminants that irritate the conjunctiva. It is crucial to clean extended wear lenses fully and as directed. If conjunctivitis has resulted, patients must throw away any contact solution, disposable lenses, eye makeup, or any other products that have come into contact with the eyes. Even glasses and cases must be disinfected thoroughly to prevent recontamination.

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