OasisEye Specialists

What causes bloodshot eyes?

What does the term bloodshot mean? It basically means the blood vessels under the eye’s surface become larger and inflamed, causing the eye to look red. Some red eyes alone are usually benign and have no reason for concern. But if the redness is accompanied with pain or loss of vision, this may indicate a serious medical problem and may need immediate medical intervention.

Listed below are some of the causes for eye redness:


One of the most common causes of redness is allergens in the surroundings. Outdoor allergens such as pollen from plants and trees. Indoor allergens consist of dust, pet fur, pet dander and even mold. The redness is often paired with itchiness, sneezing and teary eyes. This is referred to as allergic conjunctivitis, which isn’t contagious.

Dry eye

When the lacrimal glands do not produce enough tears to lubricate the eye, this can result in dry eyes. Sometimes some hormonal medications (HRT) such as estrogen can cause dry eyes as a side effect.

Subconjunctival Haemorrhage

Our conjunctiva contains many capillaries and blood vessels. If these vessels break, blood can leak into the white and the conjunctiva, which then builds up in a clump to cause subconjunctival haemorrhage. Sometimes, the simple action of coughing or sneezing can cause this to happen. People who have medical conditions such as diabetes, high blood pressure and are on blood thinners are more prone to this occurring. These bleeds may look serious, but they are usually painless and do not affect vision. It will resolve within 7-10 days.

Conjunctivitis (Pink Eye)

Conjunctivitis is the infection of the thin transparent membrane of the eye called conjunctiva. The most common ones are viral and bacterial conjunctivitis. Both are equally contagious and can spread easily. These are sometimes accompanied by a sticky discharge, watery eyes, a gritty burning sensation, sensitive to bright light or crusting of the eyelids in the morning.


This is when your eyelids are inflamed, which causes your eyelids/eyes to be swollen and red. The symptoms may be similar to those of conjunctivitis, so it is advisable to get it examined by a doctor to determine what is the cause of your red eye.


Excessive drinking of alcohol can lead to bloodshot eyes. The alcohol content causes vasodilation of blood vessels, so more blood gets filled into these dilated vessels, thus making the eye look red. Alcohol is also a type of diuretic which makes the body (and the eye) dehydrated after frequently urinating. When the eye is dehydrated, it’ll then lead to dry eyes.

Contact Lens Wear / Corneal Ulcers

People who wear contact lenses touch their eyes more often than those who do not. Thus, they are more prone to getting eye redness, if not, eye infections. Sometimes, removing contact lenses can result in scraping or scratching the cornea. Overwearing of CLs over the given timeframe may lead to neovascularization (redness). Sleeping with CLs, or unhygienic practice of cleaning CLs may lead to corneal ulcers. Action must be taken immediately if corneal ulcers arise.

Acute angle closure glaucoma

There are different types of glaucoma, but one to take note of in regards to eye redness is acute angle closure glaucoma. The redness is usually accompanied by an intense pain in the eye, haloes/rainbow rings around light, blurred decreased vision, headaches and nausea/vomiting. The iris of the eye prevents eye fluid from being drained out properly, and as the fluid builds up, this will increase eye pressure rapidly. This is usually an emergency case and has to be seen by a doctor immediately to help to bring the eye pressure down to prevent vision loss.


Episcleritis is the inflammation of the layer between the conjunctivitis and sclera. Symptoms consist of mild pain, redness and tenderness when touched. This is easily treated with artificial tears, and if needed, steroids to keep the symptoms at bay. It will usually resolve within 10 days.
On the other hand, Scleritis is the inflammation of the sclera which causes the eye to be very red. This is usually caused by an autoimmune condition, so it will need immediate medical attention. Patients will be given anti-inflammatory medication and topical steroid drops.


This is the inflammation of the middle layer of the eye called the uvea. Symptoms come in the form of pain, redness, blurred vision, and sensitivity to light. This must be treated immediately with steroids to bring the inflammation down. If not treated, it may cause retinal/choroidal scarring or even uveitic glaucoma.

Injury – trauma to the eye

Simple actions like accidentally poking your eye with your mascara applicator, or kids playing roughly and fingers poking each other’s eyes, can result in injuries to the eye. When the eye is injured, blood vessels in the eye will dilate to bring more blood cells to the site of injury to repair and heal the injury.


Spending a certain amount of time in the pool can cause bloodshot eyes as there is chlorine in the pool which then irritates the eyes.

Lack of sleep

Not getting enough sleep can also lead to red eyes. Not enough rest means no proper blood/fluid circulation, so this makes your eyes look puffy and red.


Cigarettes contain harmful toxic chemicals which are irritable for the eyes. When the eyes get in contact with these chemicals they will react and cause their eyes to be red.

All in all, as long as you have a red eye (which sometimes may be accompanied with pain, discharge or blurred vision), it is advisable to seek medical attention to determine the cause and treat it when necessary, to prevent other issues from arising.