Causes of Red Eyes

Why is your eye red?

The term "red eye" is used to describe red, bloodshot eyes. If you've ever had bloodshot eyes, you may have wondered what you did to cause your eyes to become so irritated. Many people suffer from red eye every once and awhile, but a red eye is not normal and can be caused by a number of things. If you have a red eye, it is important to find out why. A red eye can be a sign of a medical emergency. A red eye is usually painless and develops when blood vessels near the surface of the eye become enlarged and dilated. Some culprits of red eye can cause your eyes to feel inflamed and irritated, so you may find yourself seeking relief from your eye doctor. While it is always best to seek the advice of your eye doctor, you may want to try a few red eye home remedies first, at least to get a little relief.

Dry Eye Syndrome

A 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 throughout the day.


Pink Eye

Top causes of Red eye
John Rensten Collection/Stone/Getty Images

Some cases of red eye are caused by pink eye. Pinkeye, or conjunctivitis, is an inflammation or infection of the clear, protective layer that coats the front part of the eye. Pink eye can be caused by allergies, bacteria, viruses, or toxic substances. Pinkeye is very common but is usually not serious.


Blepharitis causes inflammation of the eyelid and eyelashes and may be caused by poor eyelid hygiene. Oily eyelid glands, allergic reactions, bacterial infections, or lice on the eyelashes are also common causes of blepharitis. If you have blepharitis, you may notice a gritty or burning sensation in your eyes, excessive tearing, itching, red and swollen eyelids, dry eyes, or crusting of your eyelids. The condition is not contagious and usually does not cause permanent damage to your eyesight.


Uveitis, an inflammation of the eye's uvea, can cause redness, pain, blurry vision, floaters and light sensitivity. Symptoms of this condition can occur suddenly and get worse very quickly. Uveitis should be treated quickly because other complications, such as uveitic glaucoma or retinal and choroidal scarring, may occur if it lingers.

Frequent Use of Eye Drops

Do you reach for eye drops when you wake up to red eyes? Surprisingly, frequent use of "get the red out" eye drops can actually make the eyes appear even redder. The chronic use of these eyedrops can cause “rebound dilation” of the blood vessels in the eyes, causing the eyes to appear even more bloodshot. Before instilling eye drops of any kind, it's a good idea to first consult with your eye doctor to identify the cause of your red eyes.

Contact Lens Wear

Wearing contact lenses can sometimes cause eye redness. In some people, simply having a contact lens in the eye is enough to make the eye red. If you experience discomfort while wearing contact lenses, you may want to try re-wetting drops. These eye drops are formulated for contact lenses and can provide relief for dry eyes and discomfort associated with contact lens wear.


Redness sometimes occurs with an eye injury. Injuring your eye could be as simple as sticking yourself with a mascara wand or accidentally wiping your eye with a sharp fingernail. When you injure your eye, blood vessels inside the eye enlarge and dilate to bring blood and cells to heal and repair the injury. A red eye resting from an injury is also a warning sign to let you know that something is wrong with your eye.

Corneal Ulcer or Infection

If the eye's cornea becomes infected, nearby blood vessels become enlarged and swollen, as cells rush in to help fight the infection. These cells can cause visible redness. This occurs because the cornea is avascular, meaning normally, the cornea does not have any blood vessels in it. It gets most of its oxygen and nutrients from the tears and outside atmosphere. With a corneal infection, the nearby blood vessels enlarge to get important inflammatory cells to the site quickly.

Subconjunctival Hemorrhage

A subconjunctival hemorrhage 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. 


Acute Angle-Closure Glaucoma

Sometimes a red eye can signal a serious condition. One very serious eye condition that may cause red eye is acute angle-closure glaucoma.  Acute angle-closure glaucoma is a serious medical emergency that must be treated immediately. It occurs when the fluid pressure inside the eye rises quickly. This serious type of glaucoma usually causes sudden redness in the eye, severe eye pain, and blurred vision (usually occurring in only one eye.)



 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. 


 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.


 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.


Source: Wu, Brian. "Red eyes: List of common causes." Medical News Today, 4 Mar 2017.

Continue Reading