Pink eye, or conjunctivitis, can be caused by bacteria, viruses, or allergens. Bacterial and viral forms are contagious, while allergen-based forms are not. Antibiotics can treat bacterial pink eye, while viral pink eye requires other treatments. It can be difficult to distinguish between the three forms, so it’s best to avoid casual contact with anyone showing signs of an eye infection.
The condition known as pink eye or conjunctivitis is an infection of the eyelids and a protective layer of the eye called the conjunctiva. It can be caused by bacteria that naturally reside in the eyelid, viruses that reach the eye area, or natural allergens that trigger an allergic response. Of these three main causes, only bacterial or viral infections are actually considered contagious. Conjunctivitis caused by hay fever or other allergic reactions is usually not contagious, but it is not always easy to distinguish the three forms.
The most common form of conjunctivitis is bacterial. This is because the eye lacks the usual defense mechanism to destroy harmful bacteria, such as those that reside in the roots of the eyelashes and along the edges of the eyelids. A natural chemical present in the conjunctiva is supposed to neutralize the bacteria, but this is not always successful. When the colonies manage to overwhelm the defenses of the conjunctiva, the result is the infection we know as pink eye.
The bacterial form of pink eye is indeed contagious, and around 50% of all reported cases are bacterial. Treatment is usually some form of antibiotic eye drops and scrupulous hygiene practices until the condition clears up. While the bacterial form is still producing infected fluids, however, the possibility of infecting someone else through casual contact is still present. A classroom full of students or an office full of colleagues could easily be exposed through casual contact with an infected person.
Pink eye can also be triggered by a virus, but this form accounts for only 20% of all cases. Antibiotic eye drops would have little effect on a person with viral conjunctivitis, but treatments are available that help neutralize the virus. This form is also very contagious, so the same hygiene protocols should be in place. Patients should avoid direct contact with others and any medical waste products such as bandages, tissues and droppers should be disposed of properly.
Allergens such as pollen and pollutants such as house dust can trigger a third form of conjunctivitis, which accounts for the remaining 30% of all cases. Allergen or pollutant-based pink eye treatment is usually part of a larger treatment for the underlying allergy or reaction. The itchy, swollen eyes that often accompany hay fever, for example, would be considered an allergen-based form of conjunctivitis. This form is not contagious, as the excess fluids contain neither bacteria nor viruses, just natural tear fluids and flushed out irritants.
Although nearly a third of all cases are considered non-contagious, it is not easy for the average person to distinguish contagious from non-contagious conjunctivitis. If a classmate or colleague appears to have some form of active eye infection, it’s still best to err on the side of safety and to avoid casual contact or possible transfer from handling common objects like phones or toys. When in doubt, people should use antibacterial wipes or disinfectant sprays to prevent the infection from spreading. People should avoid touching their face or eyes after coming into contact with anyone showing signs of an eye infection, with or without cold or flu symptoms.
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