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Bloodshot eye

What causes bloodshot (red) eyes?

Bloodshot eyes, sometimes known simply as red eye, are caused by blood vessels in the white of your eye (sclera) swelling up. Eyes may become bloodshot as a symptom related to an eye condition, injury, or allergy.

Sometimes bloodshot eyes just happen for no reason. They always looks a lot worse than what they are. If a bloodshot eye reoccurs, see a health care professional such as GP, for a further medical examination. It is difficult to know how serious the condition is until its cause has been diagnosed.

If your eyes are painful and stay bloodshot for longer than a few days, consult your doctor for advice. There can be many causes, and there may be more than one way to cure your bloodshot eye. The blood vessels in your eye may swell up as a result of:

  • Conjunctivitis
  • Burst blood vessel due to injury or allergy
  • Eye infections such as blepharitis
  • Improper contact lens use
  • Eye whitening drops
  • Cold and flu
  • Smoking, drinking alcohol, and drug use
  • Tiredness and dry eyes


The conjunctiva is a thin, transparent membrane that covers the outside of the eye, as well as inside the eyelids. One of the most likely reasons for red eyes is conjunctivitis. This is where the conjunctiva swells up and becomes irritated.

  • How do you get Conjunctivitis? This may due to an allergic reaction (e.g. to pollen), an infection, or by an irritant such as chlorine.
  • What to do if you have Conjunctivitis. A doctor would treat conjunctivitis after identifying the cause. They may prescribe antibiotic eye drops or antihistamines. Conjunctivitis is sometimes contagious. Make sure you're not sharing cosmetics or wash cloths. You should change your bedsheets daily after diagnosis.

To find out more about Conjunctivitis, click here.


Burst blood vessel

You may experience bloodshot eyes as a result of a burst blood vessel in your eye. Strenuous movements such as coughing or straining can cause a blood vessel in your eye to burst. This may also come about due to injury.

Medication such as aspirin may reduce the blood’s ability to clot, and can make a bloodshot eye appear very red. This often clears up on its own. If your bloodshot eye is a result of an injury, or you're experiencing pain, you should visit a doctor.

Eye infections

Eye infections can cause the blood vessels in the eye to become inflamed. You may wish to consult your doctor to help diagnose which eye infection you are suffering from. One example may be blepharitis. Blepharitis is where the area where your eyelashes grow on your eyelids swells up. This can result in redness, irritation, sensitivity to light, and eyelashes falling out. If you feel you are suffering from blepharitis, make sure you practice good hygiene. If the condition doesn’t improve, visit your doctor.

Improper contact lens use

If you wear contact lenses, you may suffer from eye redness as a result of not using them properly.

Usage. You should wash and dry your hands thoroughly before inserting or removing your contact lenses. They should be thrown away after every use if daily disposable. If monthly disposable lenses, you should store them in the correct cleaning fluid.

Lens Types. The thinner the lens, the more oxygen is able to reach your eye. You can find your lens thickness by looking at the Dk/t. If oxygen is restricted from reaching the eye, it can lead to redness. Check the type of lenses you wear are the best available. Soft lenses containing silicone hydrogel allow a large amount of oxygen to reach the eye. Ask your optician if these are available to you. To learn how to properly look after your contact lenses, click here.

Eye whitening drops

Over the counter eye whitening drops are usually taken to reduce symptoms of red eyes. Yet, overuse of these drops can lead to your eyes building up a resistance, so the drops are no longer effective. Additionally, once the drops wear off, you may find the symptoms have become worse. This is called rebound hyperaemia, and occurs because eye whitening drops restrict the blood flow in the eyes.

Cold and flu

Red eyes are a symptom of cold and flu. They are usually present during a sinus infection, particularly if you are coughing or sneezing. Eye redness should disappear after you recover from the cold or flu.

Smoking, alcohol and drugs

As well as harming many other aspects of your health, smoking can damage your eyes in many ways. Tobacco smoke is toxic to the eyes, causing irritation and redness. Additionally, alcohol causes red blood cells to bunch together. Consuming a large amount of alcohol can lead to bloodshot eyes, as well as a red complexion. Smoking marijuana causes blood vessels in the eye to dilate. This results in red eyes that can last for hours. To avoid red eyes, cut down or abstain from these substances.

Tiredness and dry eyes

Your eyes may become red if you suffer from dry eye syndrome. This is because they become irritated due to lack of lubrication. Talking to your optician may enlighten you to the correct treatment for dry eye syndrome. Often eye drops can act as artificial tears to help moisten your eyes.

Computer vision syndrome. Dry eyes can also be a result of computer vision syndrome. When looking at a computer screen, on average you will blink 66% less than when looking away. When using a computer, it can be beneficial to practice the 20-20-20 rule. This means every 20 minutes, looking away from the screen at something 20 feet away, for 20 seconds.

To read more about dry eyes, click here.

How to treat bloodshot eyes

Your bloodshot eyes may be painful. You may experience light sensitivity, swelling, or blurred vision. If so, it is important to visit an optician immediately. If your eye has become bloodshot as a result of injury, you should visit your doctor to check you have not damaged it. Many cases of bloodshot eyes clear up on their own and changes in your lifestyle can ease symptoms. Try getting more sleep, changing your diet, or taking regular computer breaks.