A sudden red patch on the white of the eye can look dramatic and cause understandable concern. In most cases, this is caused by a subconjunctival haemorrhage, a small bleed beneath the clear surface of the eye. It is usually harmless, painless, and clears up on its own within one to two weeks. While it often occurs without an obvious trigger, common causes include coughing, sneezing, eye rubbing, minor injury, or contact lens use. According to a study published in Clinical Ophthalmology, subconjunctival haemorrhage is typically benign in younger individuals, where local factors are the main cause. In older adults, however, systemic vascular conditions such as high blood pressure, diabetes, and arteriosclerosis are more commonly involved. The study also highlights that if the haemorrhage is recurrent or slow to resolve. Though usually mild, persistent cases should not be ignored. What is a subconjunctival haemorrhageA subconjunctival haemorrhage occurs when a small blood vessel breaks underneath the conjunctiva, the clear tissue that covers the white part of your eye. The conjunctiva doesn’t absorb blood quickly, so the blood gets trapped and appears as a bright red patch on the white of the eye (sclera).It might look like something from a horror film, but it’s usually painless, doesn’t affect your vision, and often clears up on its own within two weeks. In many cases, people don’t even realise it’s there until they see it in the mirror.Symptoms of subconjunctival haemorrhage to watch forThe main symptom of a subconjunctival haemorrhage is a bright red or dark red patch on the white of the eye. Other common features include:No pain or discomfortNo change in visionA mild scratchy or gritty feeling in the eyeNo discharge or swellingThere is usually no sign of injury or trauma to the surrounding area.What causes blood in the eyes Subconjunctival haemorrhages are often triggered by a sudden increase in pressure in the blood vessels. Common causes include:Sneezing or coughingVomitingStraining during lifting or using the toiletRubbing your eyes vigorouslyMinor eye trauma or injuryContact lens irritationSudden pressure changes in the head or chestSometimes, there’s no clear cause at all. These cases are called idiopathic, and they’re quite common.Who’s at riskWhile anyone can experience a burst blood vessel in the eye, certain factors can increase the likelihood:High blood pressure: Increased pressure can weaken blood vessels in the eye, making them more prone to breaking.Diabetes: Elevated blood sugar levels can damage blood vessels over time, increasing the risk of haemorrhage.Older age (especially over 65): Ageing naturally leads to more fragile blood vessels, which are more susceptible to rupture.Blood-thinning medications: These reduce the blood’s ability to clot, making even minor vessel breaks more noticeable.Blood-clotting disorders: Conditions that affect normal clotting can cause longer-lasting or more frequent eye bleeds.Improper contact lens use or hygiene: Poor lens care can irritate or injure the eye’s surface, increasing the risk of vessel rupture.Maintaining good overall health and managing chronic conditions can help lower your risk.Is blood in the eye dangerousIn the vast majority of cases, a subconjunctival haemorrhage is harmless. It doesn't affect the eye's structure or function and heals naturally over time.However, if the haemorrhage occurs repeatedly or is accompanied by other symptoms, it could be a sign of an underlying health issue, such as high blood pressure or a clotting disorder.How long does it last Most cases resolve within 7 to 14 days, similar to how a bruise fades on the skin. The redness may change colour, turning yellow or orange, before fully disappearing.Treatment and home careNo medical treatment is typically required. However, you can support healing and relieve minor irritation with:Lubricating eye drops (artificial tears)Avoiding rubbing the eyeResting the eyes from screens and bright light if they feel strainedWearing sunglasses for comfort in bright conditionsThere’s no need to avoid everyday activities unless your eye is feeling particularly irritated.When should you see a doctorWhile most cases are harmless, seek medical advice if:The red patch doesn’t fade within 2–3 weeksYou experience pain, swelling, or dischargeThere are changes in vision such as blurriness or light sensitivityThe bleeding is recurring or happens frequentlyYou are taking blood thinners or have a clotting disorderThese could point to a more serious issue that needs investigation.Prevention tipsYou can’t always prevent a burst blood vessel in the eye, but some simple steps can reduce your risk:Manage high blood pressure and diabetes effectivelyAvoid straining during physical activities or while on the toiletUse contact lenses correctly, with proper hygiene and handlingAvoid rubbing your eyesDisclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making any changes to your health routine or treatment.Also read | What causes oral cancer: Key risk factors you should know