What's Causing Your Bloodshot Eyes?

Reasons Why You Might See Red

Allergic conjunctivitis

Eye redness occurs when the blood vessels in the eye become irritated and swollen. "Bloodshot eye" is another term to describe a red eye. Red, bloodshot eyes are always alarming to see in a mirror. A bloodshot eye can appear with simply a few visible red blood vessels or can be a completely red eye. There are many reasons why your eye may appear bloodshot, but in most cases, it is red for a reason.

It is best not to overlook a bloodshot eye - your eye and your body are trying to tell you something important. If you develop bloodshot eyes, it's a good idea to have your eye doctor determine the cause. 

Dry Eye Syndrome

The most common cause of bloodshot eyes is dry eye syndrome. Dry eye syndrome occurs when there is not enough natural tears to keep the front part of the eye lubricated. When your eye becomes dry, it also becomes very red and irritated. Dry eyes can occur if you stare at the computer screen for an extended amount of time, if you don't get enough quality sleep, or if you wear your contact lenses for too long. You can also develop dry eyes from medications you take chronically. Hormonal changes occurring inside your body can also cause your eyes to become dry and irritated. Dry eyes can also develop if the glands that produce tears are plugged up with sweat and oil. If your eyes are red and bloodshot due to dry eye syndrome, it might be helpful to instill lubricant eye drops into your eyes.

Lubricant, or rewetting eye drops, are sold over the counter and can be used throughput the day.

Subconjunctival Hemorrhage

This condition causes the white part of the eye to become completely  red. It occurs when one of the blood vessels burst or breaks underneath the conjunctiva, the transparent, clear tissue that covers the white part of the eye.

The blood has no place to go, so it spreads out, like ketchup under plastic wrap. If the vessel bleeds a lot, the blood can create a bulbous subconjunctival hemorrhage in which the blood gathers so much that the eye appears swollen and pouches outward. A subconjunctival hemorrhage can look very scary, but it usually does not cause permanent harm to the eye. Straining too hard, lifting something too heavy, sneezing and coughing too hard are common culprits. 


Drinking alcohol can cause some people to develop eye redness. Alcohol can cause vasodilation, causing the vessels on the white part of the eye to become larger and more visible. Also, alcohol is dehydrating and can causes the eyes to appear red and tired.


Your eyes can become bloodshot because of allergies. Red eyes associated with burning and itching are often caused by allergies. The eyes become red because the blood vessels in the front part of the eye dilate and become larger. Fluid accumulates and causes swelling.

Acute Angle Closure Glaucoma

A more serious condition that can cause an acute red eye is acute angle closure glaucoma. This type of glaucoma is rare but it comes on suddenly, unlike most types of glaucoma which can be slow and chronic in nature.

Eye pressure rises quickly, and symptoms may develop including red eye, blurred vision, pain and vomiting. 


Another condition that can give you a bloodshot appearance is episcleritis. This is an inflammation of the thin clear layer of tissue that lies between the conjunctiva and sclera. Episcleritis causes mild eye pain and irritation along with eye redness. Sometimes the eyes become tender to the touch. Although it may go away on its own, topical steroids are often needed. 


Known for causing red, bloodshot eyes, conjunctivitis is an infection or inflammation of the conjunctiva, the clear tissue that covers the white part of the eye.

Conjunctivitis can be caused by allergies, bacterial and viruses. Viral conjunctivitis is the condition most often associated with red eyes, often called "pink eye." Viral conjunctivitis is not only very contagious, but it also causes a characteristic pink or red-colored eye in both eyes that can persist for several days to weeks.


Kunimoto, Derek Y. The Wills Eye Manual, Fourth Edition, 18 Mar 2004.

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