Conjunctivitis is inflammation of the conjunctiva, the thin mucous membrane covering the visible white part of the eye and lining the inner surfaces of the eyelids. It can result from infection, allergy, chemical irritation or other inflammatory processes. Typical features include redness, irritation, watering and discharge, although the exact pattern depends on the cause. Conjunctivitis is common and is often self-limiting, but its causes differ substantially in infectiousness, treatment and clinical significance. It should therefore not be treated as one uniform disease.
Infectious Conjunctivitis is commonly caused by viruses or bacteria. Viral conjunctivitis frequently produces watery discharge, redness and irritation and may occur alongside symptoms of a respiratory infection. Bacterial conjunctivitis can produce thicker or purulent discharge and eyelids that stick together, although clinical features overlap and cannot always reliably identify the organism. Viral forms can be highly contagious and may spread through respiratory secretions, contaminated hands and shared objects. Good hand hygiene and avoidance of sharing towels or eye cosmetics can reduce transmission.
Allergic Conjunctivitis results from an immune response to allergens and commonly causes prominent itching, watering and redness, often affecting both eyes. Seasonal allergic conjunctivitis may occur when environmental pollen concentrations increase, whereas perennial forms can be associated with year-round allergens. Unlike many infectious forms, allergic conjunctivitis is not transmitted from person to person. Management focuses on reducing allergen exposure and controlling the inflammatory response, with treatment selected according to severity and individual circumstances.
Chemical or irritant conjunctivitis can result from exposure to smoke, dust, chemicals, cosmetics or other irritating substances. Immediate irrigation is particularly important after potentially harmful chemical exposure, because some substances can damage the cornea as well as the conjunctiva. Severe pain, light sensitivity, reduced vision or persistent symptoms after chemical exposure require urgent ophthalmic assessment because the problem may extend beyond uncomplicated conjunctivitis. The degree of redness alone does not reliably indicate the severity of ocular surface injury.
Diagnosis is usually clinical and involves assessing the pattern of redness, discharge, itching, pain, visual acuity and associated symptoms. Examination should consider whether the cornea, anterior chamber or other structures are involved. Severe pain, significant photophobia, reduced vision, corneal opacity, trauma or contact-lens-associated symptoms can indicate conditions more serious than uncomplicated conjunctivitis. Contact lens wearers require particular caution because corneal infections can progress rapidly and threaten vision.
Treatment depends on the cause. Viral conjunctivitis generally requires supportive care rather than antibiotics, because antibiotics do not treat viruses. Some bacterial cases may benefit from topical antibiotics, while allergic conjunctivitis can be managed with measures directed at the allergic inflammatory response. Unnecessary antibiotic use can cause adverse effects and contributes to inappropriate antimicrobial exposure. Sharing prescription eye drops is inappropriate because treatment should match the actual diagnosis and some preparations can worsen particular conditions.
Conjunctivitis is frequently confused with other causes of red eye, including keratitis, uveitis, acute glaucoma and significant ocular injury. A relatively mild gritty sensation and discharge may fit conjunctivitis, whereas marked pain, photophobia or visual loss should prompt consideration of alternative diagnoses. Contact lens wear increases concern for microbial keratitis. The distinction matters because some serious eye diseases can initially present primarily as redness, while inappropriate self-treatment can delay appropriate care.
Most uncomplicated conjunctivitis does not cause permanent visual loss, but exceptions exist when infection involves the cornea or when a more serious condition has been incorrectly labelled as conjunctivitis. Infectious cases can spread rapidly in households, schools and workplaces, making hand hygiene and avoidance of sharing personal items useful. Persistent, recurrent or severe symptoms should be medically assessed rather than repeatedly treated empirically. The term therefore describes an anatomical inflammation rather than a single infectious diagnosis.
