Pink eye, clinically known as conjunctivitis, is a common condition involving inflammation of the transparent membrane covering the white part of the eye and the inner surface of the eyelids. This inflammation causes the eye to appear reddish or pink. Identifying the underlying cause—viral, bacterial, or allergic—is important because it dictates the appropriate management and necessary steps to prevent transmission.
Comparing the Key Symptoms
The most telling difference between viral and bacterial conjunctivitis lies in the nature of the discharge produced. Viral infections typically result in a thin, watery, and clear discharge, often described as excessive tearing. Due to this watery consistency, the eyelids may only lightly stick together upon waking, if at all.
Bacterial infections, by contrast, frequently produce a thick, gooey discharge that is yellow, green, or opaque greyish. This purulent discharge often causes the eyelashes and eyelids to crust over severely, making it difficult to open the eyes, particularly in the morning. The discharge from a bacterial cause is generally more profuse and persistent throughout the day.
Another distinguishing factor is how the infection begins and spreads. Viral conjunctivitis often starts in one eye and rapidly spreads to the second eye within a day or two, reflecting its highly contagious nature. It is also commonly associated with symptoms of a concurrent upper respiratory infection, such as a cold or flu.
Bacterial conjunctivitis, while still contagious, frequently starts and may remain more severe in a single eye, though it can affect both. Systemic illness, such as a cold, is rarely a preceding or accompanying symptom. Viral infections tend to cause a gritty or burning sensation, while bacterial cases can involve more pronounced eyelid swelling and irritation.
Management and Contagion
The management strategy depends entirely on whether the cause is viral or bacterial, as antibiotics are only effective against bacterial pathogens. Because the majority of viral cases are caused by adenoviruses, there is typically no specific medical treatment available. Viral conjunctivitis is usually self-limiting, resolving on its own within one to two weeks, though some cases can persist for up to three weeks.
Management for the viral form focuses on supportive care, including using artificial tears to soothe the eye surface and applying cool compresses to reduce swelling and discomfort. Conversely, treatment for bacterial conjunctivitis often involves prescription antibiotic eye drops or ointments, which target responsible organisms like Staphylococcus aureus or Streptococcus pneumoniae. While many mild bacterial cases resolve without medication, antibiotics can accelerate recovery.
The level of contagion also varies between the two types. Viral conjunctivitis is highly contagious, spreading easily through contact with infectious tears, respiratory droplets, or contaminated surfaces. Patients are typically contagious as long as they have watery discharge or excessive tearing.
Bacterial conjunctivitis is also contagious, transmitted through hand-to-eye contact or shared objects. However, the infection is often controlled quickly once medication is started. A person is typically cleared to return to work or school 24 hours after beginning antibiotic treatment, provided there has been significant clinical improvement. Good hygiene practices, such as frequent hand washing, are necessary to prevent the spread of both types.
Allergic Conjunctivitis as a Differential
Allergic conjunctivitis is a common, non-infectious form of pink eye that must be considered when evaluating symptoms. Unlike the infectious types, allergic cases are caused by an immune response to environmental triggers such as pollen, pet dander, or mold. The primary symptom distinguishing allergic conjunctivitis is intense, bilateral itching.
This type of pink eye affects both eyes simultaneously and is often seasonal or immediately follows exposure to a known allergen. The discharge is characteristically thin and watery, similar to viral cases. However, the condition is not accompanied by cold or flu symptoms and is not contagious. The lack of contagiousness and the presence of severe itching are helpful indicators when ruling out a viral or bacterial cause.
Signs Requiring Immediate Medical Attention
While most cases of pink eye are mild and resolve without permanent damage, certain symptoms indicate a potentially more serious underlying condition requiring immediate professional evaluation. Severe pain inside the eye is a warning sign that the inflammation may have spread beyond the conjunctiva to deeper structures.
Any sudden change in vision, such as blurriness not just due to discharge, or increased sensitivity to light (photophobia) warrants urgent medical attention. These symptoms can suggest involvement of the cornea, the clear front surface of the eye, which can lead to scarring and permanent vision changes if left untreated. Symptoms that worsen after several days or fail to improve after a week of supportive care also necessitate an evaluation. Any signs of pink eye in a newborn infant less than 30 days old should be seen by a medical professional immediately.