Conjunctivitis, commonly called “pink eye,” is inflammation of the thin, transparent membrane (the conjunctiva) covering the white part of the eye and inner eyelid. Small blood vessels in the conjunctiva become swollen and visible when irritated, causing the characteristic pink or red appearance. While infections are frequently responsible, many other eye conditions share the primary symptoms of redness, discomfort, and tearing. Distinguishing infectious pink eye from these mimics is important because their causes, treatment, and contagiousness vary significantly.
Allergic Reactions and Environmental Irritants
One common cause of eye redness that is not infectious pink eye is allergic conjunctivitis, where the immune system overreacts to a harmless substance. Airborne triggers like pollen, pet dander, or mold spores cause the body to release histamine, which dilates blood vessels and irritates nerve endings. This reaction results in intense itching, the hallmark symptom distinguishing allergic reactions from most infections.
Allergic conjunctivitis typically affects both eyes simultaneously. The discharge is usually thin, watery, and clear, unlike the thick, sticky discharge common with bacterial infections. Symptoms often appear seasonally or immediately following exposure to a known allergen. Since this is an immune response, it is not contagious.
The eye can also be irritated by non-allergenic substances, leading to temporary irritant conjunctivitis. Exposure to chemicals like chlorine, smoke, smog, or harsh soaps can cause immediate redness and a burning sensation. These symptoms are acute and resolve quickly once the irritant is flushed out, usually through natural tearing or rinsing with water. This irritation does not involve a pathogen and will not spread.
Chronic Surface Conditions
Persistent or recurring redness and irritation may signal chronic surface conditions requiring ongoing management. Dry Eye Syndrome (keratoconjunctivitis sicca) occurs when the eyes do not produce enough tears or tears of sufficient quality for proper lubrication. This lack of adequate tear film causes friction, resulting in a gritty or sandy sensation, burning, and sometimes temporary blurring of vision that improves with blinking.
Paradoxically, dry eye can sometimes cause excessive watering, a reflex response to surface irritation. The eye produces low-quality, watery tears that fail to soothe the surface. Symptoms often worsen throughout the day, particularly after long periods of focused work like reading or using a computer screen.
Another common chronic mimic is blepharitis, the inflammation of the eyelid margins often caused by a buildup of skin cells, oil, and bacteria near the base of the eyelashes. This condition is not contagious but leads to chronic redness, particularly along the eyelid edges. A distinguishing sign is the presence of flaky, dandruff-like scales or crusting along the lashes, which may cause the eyelids to feel sticky in the morning. Blepharitis requires consistent hygiene, such as warm compresses and gentle cleansing, as it is an ongoing issue of gland dysfunction.
Warning Signs of Severe Eye Conditions
While most causes of a red eye are benign, certain symptoms mimicking pink eye can signal serious conditions requiring immediate medical attention.
Corneal Abrasion
A corneal abrasion, a scratch on the clear front surface of the eye, causes intense, sudden pain and the sensation that something is lodged in the eye. Unlike the general discomfort of conjunctivitis, an abrasion usually involves significant light sensitivity (photophobia) and excessive tearing in one eye following a known or suspected trauma.
Iritis (Uveitis)
Inflammation deeper within the eye, such as iritis (a form of uveitis), presents with more severe symptoms than typical surface irritation. Iritis is characterized by deep, aching eye pain, severe photophobia, and sometimes a change in pupil size or shape. The redness tends to be concentrated in a ring immediately surrounding the iris, a pattern known as ciliary flush, which differs from the diffuse redness of conjunctivitis.
Angle-Closure Glaucoma
Angle-closure glaucoma occurs when the eye’s drainage system becomes suddenly blocked, leading to a rapid and dangerous spike in internal eye pressure. This condition is marked by the sudden onset of severe eye pain, a throbbing headache on the same side, nausea, vomiting, and seeing blurred vision or colored halos around lights. Any combination of severe pain, vision loss, or intense light sensitivity warrants immediate consultation with an eye care professional.