What is conjunctivitis?
Conjunctivitis is inflammation of the clear membrane covering the white of the eye and the inside of the eyelids. It can be infective, allergic or irritant, and the treatment differs substantially between those.
- Subject
- Eye conditions
- Topic
- Infections, allergies & injuries
- Kind of question
- What is…
- Last reviewed
- 22 September 2026
In more detail
Because the causes look similar, a red eye that is painful, light sensitive or associated with reduced vision is assessed rather than assumed to be simple conjunctivitis.
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It is one of 483 answers in the vision and eye health knowledge base, filed under Eye conditions & diseases in Infections, allergies & injuries . The subject page carries the answers either side of it, and the hub is searchable.
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This information is for educational purposes and does not replace an examination by a qualified eye-care professional.
General answers cannot tell you what is happening in your own eyes. Only an examination by a qualified ophthalmologist can do that.
Sources & further reading
We prefer primary sources. Where a claim comes from a manufacturer, a single study or a regulator, it is labelled as such below.
- Eye Health Information
Condition-by-condition eye health information from a US government research institute, written for patients rather than for clinicians.
Used for Plain-language explanations of eye conditions and their symptoms; Healthy vision and screening guidance.
Link checked 23 September 2026
- EyeSmart: eye health information for the public
Patient-facing material from the largest ophthalmology professional body, covering conditions, tests and treatments outside refractive surgery.
Used for Cross-checking patient-facing explanations of non-refractive eye conditions; Describing what tests such as dilation and OCT involve.
Link checked 23 September 2026