Conjunctivitis, commonly known as pink eye, is the inflammation of the conjunctiva, the thin, clear membrane covering the white part of the eye and the inner surface of the eyelids. This inflammation causes the characteristic redness, irritation, and sometimes discharge. While pink eye is usually a minor, standalone condition, it can sometimes be a manifestation of a deeper, underlying health issue. Understanding this difference is important for appropriate treatment.
Establishing the Norm: Typical Conjunctivitis Causes
The majority of pink eye cases are caused by highly contagious, localized infections or environmental triggers. The most frequent cause is a viral infection, often stemming from the adenoviruses responsible for the common cold. Viral conjunctivitis typically presents with a watery discharge, usually beginning in one eye and sometimes spreading to the other.
Bacterial conjunctivitis produces a thicker, pus-like discharge that is yellow or green, often causing the eyelids to stick together upon waking. Allergic conjunctivitis is not contagious and is triggered by environmental allergens like pollen or pet dander, characterized by intense itching in both eyes, excessive tearing, and sometimes accompanying nasal allergy symptoms.
Pink Eye as a Sign of Systemic Illness
When conjunctivitis is persistent, severe, or accompanied by other body-wide symptoms, it may signal an underlying systemic disease. Autoimmune disorders often involve the eyes because the immune system mistakenly attacks healthy tissues. Systemic Lupus Erythematosus (SLE) causes inflammation throughout the body and can manifest with conjunctivitis or severe dry eye.
Rheumatoid Arthritis, which primarily affects the joints, is frequently associated with keratoconjunctivitis sicca (severe dry eye). This chronic lack of lubrication causes redness and irritation easily mistaken for infectious pink eye.
Infectious Systemic Causes
The group of conditions known as seronegative spondyloarthropathies, including Reactive Arthritis, can cause a triad of symptoms: arthritis, urethritis, and conjunctivitis. Infectious agents that affect the entire body can also manifest in the eye. Certain sexually transmitted infections (STIs) can cause conjunctivitis, particularly in newborns exposed during birth, requiring specific treatment.
Specific viral syndromes, such as Measles or COVID-19, have also been recognized as potential causes of conjunctival inflammation during the course of the systemic illness. In these cases, the eye symptom is part of a larger, body-wide health issue requiring comprehensive medical attention.
Localized Conditions That Mimic Pink Eye
Not all red eyes are true conjunctivitis; several non-infectious, localized eye problems can produce similar symptoms. A subconjunctival hemorrhage occurs when a small blood vessel breaks beneath the eye’s clear surface. This results in a vivid, localized, bright red patch that is typically harmless and resolves on its own, unlike the diffuse redness of true pink eye.
Severe dry eye syndrome (keratoconjunctivitis sicca) causes chronic irritation, redness, and a gritty sensation due to inadequate tear production. This chronic condition requires ongoing management rather than short-term treatment.
Other Mimics
Blepharitis, or inflammation of the eyelids often at the lash line, causes flaking, crusting, and generalized redness that can be confused with a bacterial infection. Corneal abrasions (scratches on the clear front surface of the eye) also cause intense redness, pain, and a foreign body sensation. Exposure to environmental irritants like chemical fumes or chlorine can cause immediate redness and discomfort that clears once the irritant is removed. Misidentifying these localized conditions can lead to delayed or inappropriate treatment.
Warning Signs Requiring Urgent Care
While many cases of pink eye are minor, certain symptoms indicate a more serious condition requiring immediate medical evaluation. Severe eye pain that goes beyond simple irritation is a red flag, often suggesting inflammation deeper within the eye, such as uveitis or keratitis.
Sudden changes in vision, including new blurriness or heightened sensitivity to light (photophobia), are signs that the cornea or internal eye structures may be affected. A thick, green, or yellow discharge that rapidly accumulates may indicate a severe bacterial infection. Furthermore, if pink eye is accompanied by systemic symptoms such as a high fever, severe headache, or a widespread rash, it may suggest a serious systemic infection or inflammatory disease. These combinations warrant immediate care to prevent potential vision loss.