Red eyes: when is it harmless and when is it not?

The red patch: a burst vessel

A sharply demarcated, evenly bright-red patch on the white of the eye — often discovered in the morning, painless, vision unchanged? That is almost always a subconjunctival haemorrhage: a burst capillary under the conjunctiva, the eye's equivalent of a bruise. Straining, sneezing, coughing or rubbing can cause it, and often there is no identifiable reason at all. It looks impressive, is harmless, and fades within one to two weeks. Only when it recurs without reason, or happens often while you use blood thinners, is it worth discussing with your GP.

Both eyes red, burning or itching

Diffuse redness in both eyes with burning, grittiness or itch fits the big three: dry eyes, irritation (smoke, chlorine, wind, screen work) and allergy. Itch as the main complaint points strongly to allergy, certainly with sneezing or an itchy nose alongside. These causes are bothersome but not threatening; artificial tears, cool compresses and antihistamines for allergy usually help well.

One red eye with discharge

A red eye with sticky lids (glued shut in the morning) and pus or mucus fits infectious conjunctivitis. It is usually viral and self-limiting; hygiene (hand washing, own towel) limits spread. With copious pus, little improvement after a week, or fragile health, the GP can take a look and prescribe drops if needed. We have a separate, more detailed explainer on conjunctivitis.

The signs that change the story

There is a small set of combinations where a red eye is not a matter of waiting it out. Remember them as questions: Does it really hurt (deep pain, not just burning)? Is bright light hard to tolerate? Do you see blurrier than normal? And: do you wear contact lenses?

Pain plus light sensitivity fits inflammation deeper in the eye (such as uveitis) or a corneal injury. A red eye in a contact lens wearer always deserves a low threshold: a corneal infection can move fast and the lens must come out immediately. And the rare but urgent outlier: one red, hard-feeling eye with severe pain, blurred vision, halos around lights and nausea — that picture fits an acute glaucoma attack and is a reason to call your GP or the out-of-hours service straight away.

What can you do yourself?

For burning, irritated eyes: artificial tears (preservative-free if used often), no rubbing, pause make-up and lenses. For allergy: cool compresses and antihistamines if needed. What to avoid: 'redness relief' drops that constrict vessels — they mask the picture, dry the eye further and cause rebound redness when you stop. And with any of the warning signs above: don't doctor it yourself — have it looked at.