Conjunctivitis can be caused by viruses, bacteria, allergies or irritation. Treatment and precautions depend on the cause.
What is conjunctivitis?
Conjunctivitis, often called pink eye, is inflammation of the thin tissue covering the white of the eye and lining the eyelids. It may affect one or both eyes. Several different causes can look similar, so redness alone cannot tell you which treatment is appropriate. CDC overview
Symptoms and important warning signs
Typical symptoms include redness, watering, itching, burning, grittiness and discharge that may crust around the lashes. Eyelids can appear puffy.
Seek urgent eye assessment for significant pain, light sensitivity, reduced vision or a very red eye. Contact-lens wearers with a red or painful eye need prompt assessment for corneal infection. A newborn with red, swollen or sticky eyes should be assessed immediately. Sudden loss of vision is an emergency. NEI guidance | NHS guidance | NHS red-eye guidance
Causes and risk factors
Viruses and bacteria can cause infectious conjunctivitis. Allergens, such as pollen, and irritants, such as smoke or cosmetics, can also inflame the eye surface. Viral and bacterial forms can spread easily; allergic conjunctivitis is not contagious. Recent respiratory illness, exposure to someone with infectious conjunctivitis and contact-lens use are useful details to discuss. CDC | NEI
How is it diagnosed?
A clinician asks about symptoms, exposure, allergies, lens wear and how the problem developed, then examines the eyes. Tests are sometimes needed. A painful red eye may have a different cause, including corneal infection or uveitis, so avoid diagnosing yourself from a photograph. NEI assessment information
General treatment and hygiene
Treatment depends on the cause. Antibiotics may be prescribed for bacterial infection, but they do not treat viral or allergic conjunctivitis. Allergy treatment or soothing measures may be appropriate in other cases. Many uncomplicated cases settle without specific medicines, but worsening or persistent symptoms should be reviewed. NHS treatment information
Wash hands regularly, avoid rubbing your eyes and do not share towels, pillows, eye drops or makeup. Stop contact-lens wear while symptomatic and ask when it is safe to restart. Follow advice about cleaning or replacing lenses and cases used during infection. CDC prevention guidance
Conjunctivitis: Pink Eye, Causes and Safe Next Steps illustrated
Questions for your appointment
- What is the likely cause, and is there a reason to test it?
- Is medicine needed, or would supportive care be appropriate?
- When can I return to contact lenses, school or close-contact work?
- What should I do if pain or blurred vision develops?
Frequently asked questions
Is every red eye contagious?
No. Allergies and other non-infectious conditions can also cause redness. CDC
Do I always need antibiotic drops?
No. Their usefulness depends on whether a bacterial infection is suspected. They do not treat viruses. NHS
Must I stay home from school or work?
Advice depends on symptoms, close-contact activities and local policy. Ask your clinician and school or employer rather than assuming one rule applies everywhere. CDC
This information is educational and cannot confirm why an eye is red.
Sources and further reading
- CDC: About Pink Eye
- National Eye Institute: Pink Eye
- NHS: Conjunctivitis
- CDC: How to Prevent Pink Eye
- NHS: Red eye
General educational information prepared October 2026. Treatments described are general options; availability and suitability require an individual assessment.
