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Bloodshot eye

What causes bloodshot eyes?

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We’ve all been there – your eyes suddenly become bloodshot and you look like you’re auditioning for a part as an extra in The Walking Dead. Fear not, it’s not an unusual occurrence and most of the time things look far worse than they are.

The reason why bloodshot eyes occur is due to swelling of the blood vessels in the white area of your eye (the sclera). This could have no relatable cause, or it could be due to an eye condition, injury or an allergy.

If a bloodshot eye does happen to regularly reoccur, we’d suggest checking in with a health care professional for a further medical examination, as it can be difficult to know how serious the condition is until the underlying cause has been diagnosed.

Affecting factors

Although the main cause is swelling of the blood vessels, there can be many additional contributing factors. We’ve short-listed the most common, and if you’d like to know more about each one and how you can treat it, read on further below:

  • Conjunctivitis
  • 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

Blue eye

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One of the top likely causes behind red eyes, conjunctivitis is a condition where the conjunctiva swells and becomes irritated. The conjunctiva is a thin, transparent membrane that covers the outside of the eye and the inside of our eyelids.

You may experience conjunctivitis as a result of an allergic reaction, an infection or from a chemical irritant such as chlorine. It’s a contagious condition, so be sure that you don’t share cosmetics, face towels or pillows. Once the cause is identified, your doctor is likely to prescribe antibiotic eye drops or antihistamines. You can maintain good eyelid hygiene by using a warm, clean cotton wool pad to gently rub your eyelashes to remove any debris.  

Eye infections

Eye infections can cause the blood vessels in the eye to become inflamed. Blepharitis, for example, is where edge of the eyelids become irritated and sore. This can result in redness of the eye, sensitivity to light, and eyelashes falling out. If you feel you are suffering from blepharitis, make sure you practice good hygiene.

Improper contact lens use

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

You should wash and dry your hands thoroughly before inserting or removing your contact lenses. If they’re daily disposables, make sure you’re throwing them away at the end of each day and not reusing them. If you’re a wearer of monthly disposable or extended wear lenses, ensure that the correct cleaning and storing regimen is being followed.

Contact lens thickness is different for every product. The thinner the lens, the more oxygen is able to reach your eye. If the oxygen supply is restricted, it can lead to redness. If you feel like your contact lenses might be causing the problem, check with your optician that you’re wearing the best possible product for you.

Eye whitening drops


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Over the counter eye whitening drops are usually taken to reduce symptoms of red eyes and make your eyes sparkle. Yet, overuse of these drops can lead to your eyes building up a resistance, reducing how effective the product is. Once the product wears off, it can actually make red eyes worse. This is called rebound hyperaemia, and occurs because eye whitening drops restrict the blood flow in the eyes.

Cold and flu


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Bless you. And again! If you’re suffering from a cold or flu, then it’s likely red eyes will appear too – particularly if you’re repeatedly coughing or sneezing. Over the counter medication can help relieve symptoms, and the redness should disappear once you’re on the road to recovery.

Smoking, alcohol and drugs

Pouring beer

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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.

When you drink alcohol, it causes red blood cells to bunch together and after a couple of drinks at the local, you may find yourself stumbling home with bloodshot eyes, as well as a red complexion.

Smoking marijuana causes blood vessels in the eye to dilate which results in red eyes that can last for hours and so it’s probably best to stay away.

Tiredness and dry eyes

Woman sleeping

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Your eyes may also become red if you suffer from dry eye syndrome or if you haven’t been getting enough sleep. Your eyelids will go into overdrive as they try to blink more to provide increased lubrication to your eyes. Most eye drops can act as artificial tears which helps to moisten your eyes. If you’ve been binging Netflix and staying up late, we’d also suggest getting a good night’s sleep.

Look after your peepers!

Bloodshot eyes can be painful, and you may experience light sensitivity, swelling, or blurred vision. If this is something you’re suffering, it is important to visit an optician immediately. If the reason your eyes are red is due to an 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, so try getting more sleep, make changes to your diet and maintain good hygiene, for example.