What are the Causes of Conjunctivitis?

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  • Written By: Dorothy Bland
  • Edited By: Melissa Wiley
  • Last Modified Date: 15 August 2019
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Infectious causes of conjunctivitis include viruses and bacteria, while noninfectious causes include allergies and chemical irritants. The eye condition is an inflammation that affects the membranes of the interiors of the eyelids and the white membranes of the eyes. All forms of conjunctivitis have certain symptoms in common, mainly irritated, itchy, and watery eyes. Specific symptoms are also likely to appear that correspond to the primary cause of the infection.

Viruses are the most likely cause of conjunctivitis, and the group of viruses most liable to be accountable are adenoviruses. Adenoviruses are a group of viruses responsible for a number of upper respiratory diseases, including a form of the common cold and bronchitis. Viral conjunctivitis is the form commonly known as pink eye because it normally causes the whites of the infected eyes to appear pink or red. Usually viral conjunctivitis will present with a clear or white discharge. Swollen eyelids and sensitivity to light might also be present. Other viral symptoms, such as a runny nose or a sore throat, might also occur.


Just as viruses are responsible for viral conjunctivitis, bacterial conjunctivitis is caused by any of a number of bacterial organisms. One likely culprit is streptococcus, a group of bacteria that causes strep throat, scarlet fever, and a number of other diseases. Another of the bacteria-based causes of conjunctivitis is Haemophilus influenzae. The bacteria often causes an ear infection at the same time. With bacteria conjunctivitis, eye discharge is usually sticky, thick, and has a yellow-greenish appearance. The eye may also feel gritty and often sticks together or become crusted, especially after opening up the eyes after sleeping.

When the eyes are exposed to any allergy-causing agents, such as animal dander, perfume, or pollen, allergic conjunctivitis is a possibility. Such allergic reactions often occur in those with a family history of allergies and in individuals who suffer from hay fever, asthma, or other allergy-based diseases. The condition may cause more intense itching than infectious causes of conjunctivitis and can produce greater tear production. With allergic conjunctivitis, the eyelids will often appear swollen. The eyes may also burn and produce a stinging discharge.

If the eyes are exposed to irritating substances, such as chlorine from a swimming pool, a form of conjunctivitis frequently called chemical or toxic conjunctivitis could arise. Possible chemical causes of conjunctivitis include chemicals that are splashed into the eyes as well as smoke or fumes that enter the eyes. Often, the eye can be flushed with water for several minutes to remove the irritation and redness. In some instances, however, toxic substances can cause considerable swelling, severe pain, and decreased vision.

Some of the other possible causes of conjunctivitis include sand stuck in the eye or a scratched eye. Neonatal conjunctivitis, a type occurring in newborns, has a range of probable causes, including plugged tear ducts. Some of the more serious causes of neonatal conjunctivitis include gonorrhea and chlamydia. The sexually transmitted diseases can be transferred to the newborn during the delivery process.

As a rule, conjunctivitis is considered a symptom and not a disease. Normally, the condition does not lead to vision loss and will generally clear up once proper treatment has been received. Some of the forms of conjunctivitis, however, have serious underlying causes and could threaten vision if not promptly treated. Seeking medical attention is commonly recommended to determine the causes of conjunctivitis and to receive accurate treatment and relief from the condition.



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