A red eye can be alarming, but is often just a sign of a minor eye condition, such as conjunctivitis or a burst blood vessel. If it's painful, there may be a more serious problem. 

See your GP for advice if your red eye doesn't start to improve after a few days.

Contact your GP or NHS 111 immediately, or go to your nearest accident and emergency (A&E) department, if:

  • you have a painful red eye
  • you have other symptoms, including reduced vision, sensitivity to light, a severe headache and feeling sick
  • you recently injured your eye – particularly if something has pierced your eye

This page aims to give you a better idea of what might be causing your red eye. However, it shouldn't be used to self-diagnose your condition. Always see a doctor for a proper diagnosis and treatment.

Common causes of a painless red eye

The most likely causes of a painless red eye are minor problems such as conjunctivitis or a burst blood vessel. These conditions don't tend to affect your vision and normally get better within a week or two.


Conjunctivitis is inflammation (swelling and irritation) of the conjunctiva – the thin layer of tissue covering the eyeball and inner surfaces of the eyelids.

This causes the blood vessels on the eye to swell, making one or both eyes look bloodshot and feel gritty.

Other symptoms can include itchiness and watering of the eyes, and a sticky coating on the eyelashes.

Conjunctivitis can be caused by an infection, an allergy (for example, to pollen), or an irritant, such as chlorine or dust.

Treatment will depend on what is causing the condition. Sometimes no treatment is needed, because it may get better on its own. 

Your doctor may recommend:

  • regularly cleaning away any crusting or discharge
  • not wearing contact lenses until the condition passes
  • washing your hands regularly and avoiding sharing pillows or towels to help prevent the condition spreading to others (if it's infectious)
  • antibiotic eye drops for bacterial infections or medications, such as antihistamines for allergies

Read more about treating conjunctivitis.

Burst blood vessel in the eye

Straining, coughing or injuring your eye can sometimes cause a blood vessel to burst on the eye surface, causing a bright red blotch. This is called a subconjunctival haemorrhage.

It can look alarming, especially if you're taking medication such as aspirin or warfarin (these reduce the blood's ability to clot, which can exaggerate the redness), but it's not usually serious and should clear up on its own within a few weeks.

Common causes of a painful red eye

If your red eye is painful or you have other symptoms such as reduced vision, the cause is likely to be one of the below conditions.

These conditions can sometimes be serious and could threaten your sight, so they should be assessed by a doctor as soon as possible.


Iritis is inflammation of the iris (the coloured part of the eye). It's also known as anterior uveitis.

As well as a red eye, you may notice that your eye is sensitive to light, your vision is blurred and you have a headache.

Often, no cause is identified, although iritis can sometimes be caused by an underlying problem with the immune system or an infection.

Iritis usually responds quickly to treatment with steroid medication to reduce the inflammation. It rarely leads to severe problems.

Acute glaucoma

Acute glaucoma is a serious condition where there is a sudden increase in pressure inside your eye. Your eye will probably be severely red and painful, and you may feel sick and see halos around lights. Your vision may be blurred or cloudy.

If your GP thinks you may have acute glaucoma, they will refer you to an eye specialist (ophthalmologist) immediately, because the condition could potentially lead to permanent loss of vision if it's not treated quickly.

An ulcer on the cornea

An ulcer on the cornea (the clear outer layer at the front of the eyeball) is usually caused by a bacterial or viral infection. It can cause the eye to become red and sensitive to light, and it can feel like there's something in your eye.

Bacterial corneal ulcers are usually seen in people who wear contact lenses. Viral corneal ulcers are often seen in people who frequently get cold sores.

If your GP thinks you have a corneal ulcer, they will refer you to an eye specialist for treatment.

A scratch to the cornea or particle in the eye

A red and painful eye can sometimes be caused by a particle, such as a piece of grit, getting in your eye.

If there's something in your eye, your GP or a hospital doctor at an accident and emergency (A&E) department will try to remove it. They will first put anaesthetic eye drops into your eye to numb it and reduce any pain.

If the particle has scratched your eye, it may feel a bit uncomfortable when the anaesthetic eye drops have worn off. You may be given antibiotic eye drops or ointment to use for a few days to reduce the risk of infection while it heals.

Read more about eye injuries.

Page last reviewed: 26/05/2015

Next review due: 26/05/2017