Why does conjunctivitis cause red eye?

Red Eye is a very common presentation of Conjunctivitis. The redness may affect one eye first and later involve the other, depending on the trigger.

The conjunctiva is a clear layer over the white of the eye and inside the eyelids. Infection, allergy, irritation, or a reaction to an eye product can inflame this layer. Along with redness, there may be watering, discharge, a gritty feeling, or itching. The pattern of associated symptoms helps a clinician distinguish conjunctivitis from other eye conditions.

Wash hands often and avoid touching or rubbing the eyes. Use a cool clean compress for comfort, and use a separate clean towel or pad for each eye. Do not share towels, pillows, or eye makeup. Contact-lens wearers should remove their lenses and ask a clinician when it is safe to use them again. Avoid using someone else's eye drops.

Get urgent medical care for a painful red eye, reduced vision, significant light sensitivity, a severe headache with nausea, injury, or a chemical splash. Prompt assessment is also important for a contact-lens wearer with a red painful eye. Arrange review if the redness is worsening, spreading with eyelid swelling, or not settling as expected.

Ask whether the redness appears related to infection, allergy, or another source of irritation. Describe discharge, itching, pain, light sensitivity, any vision changes, contact-lens use, and recent exposure to new cosmetics or workplace irritants.