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What causes red eyes? Related conditions and treatments

Medically reviewed by Leslie Greenberg, MD
Board-Certified Family Physician
Updated Nov. 17, 2023  •  Published Jun. 20, 2023
Fact Checked
Causes of red eyes

Overview: What do red eyes look like?

The eyes can get irritated, infected, or injured like any other body part. The body immediately starts to fix the problem and begins to swell. Blood vessels near the affected area get wider, allowing more blood to flow to the site. That produces the characteristic appearance of “bloodshot eyes”: highly visible blood vessels on the whites of the eyes. That’s usually what people mean when they use the term red eyes, but sometimes the eyes turn red because of bleeding. For some, the only symptom is bloodshot eyes. Still, in other cases, there may be additional symptoms like itchiness, tenderness, crusting, discharge, or an aggravating feeling that sand is on the eye's surface. Eye pain, sensitivity to light, blurry vision, and other vision changes are more ominous symptoms that can accompany red eyes. In those cases, it’s important to see a healthcare provider. 

RELATED: What causes eye pain? Related conditions and treatments

Key takeaways:

  • Red eyes are a common symptom of irritation, allergies, foreign bodies, eyelid swelling, infection, injury, autoimmune disorders, or angle-closure glaucoma may cause.

  • Red eyes do not require immediate medical attention unless there’s blood in the eye or other symptoms such as pain or vision changes.

  • Red eyes generally do not require treatment, but some types do. Red-eye typically resolves without treatment in some cases and with treatment in others. How long that takes depends on the cause.

  • Treatments of red eyes vary by cause. Read more about treatments for pink eye here, blepharitis treatments here, and allergy treatments here.

  • Red eyes can be managed with artificial tears, cool compresses, reducing screen time, avoiding allergens, staying out of pools, and taking a break from wearing contact lenses.

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What causes red eyes?

The most common causes of red eyes are irritation, allergic reactions, infections, and minor injuries. When just the eye's transparent outer layer (the conjunctiva) is affected, the condition is called conjunctivitis or “pink eye.” Conjunctivitis is the most commonly experienced type of red eye, accounting for about 80% of cases. Cornea problems, inflammation of the inner eye tissues, or other serious eye conditions can also cause red eyes.

The most common causes of conjunctivitis are:

  • Irritation of the surface of the eye (rubbing the eye, dry eye, dust, smoke, contact lenses, blepharitis)

  • Allergic reactions

  • Toxins

  • Bacterial infections

  • Viral infections

  • Other types of infections 

The cornea is the transparent tissue above the pupil and iris. The most common causes of corneal conditions that cause red eyes include:

  • Foreign bodies

  • Minor scratches or injuries

  • Herpes infection

  • Bacterial infections

  • Sunlight (UV rays)

The most common causes of inflammation of the inner lining of the eye (uveitis) and the whites of the eyes (scleritis) are:

  • Injury

  • Autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, lupus, scleroderma, and others

  • Bacterial, viral, or parasitic infections (corneal ulcer)

Other causes of red eyes include:

  • Bleeding 

  • Angle-closure glaucoma

  • Deep bacterial infections

RELATED: Pink eye vs. allergies: compare types of pink eye

Should I be worried about red eyes?

Most cases of red eye do not require treatment. However, if red eye does not improve in a week or is accompanied by crusting discharge or sensitivity to light, see a healthcare provider. In those cases, there may be a more serious issue at work, such as infection, injury, or something worse. Get immediate medical care if red eye is accompanied by other symptoms such as eye pain, fever, blurred vision, halos, or other vision changes. If the bleeding or a tear that goes through the eye is noticeable, go to an emergency room. Some conditions that cause red eyes can rapidly progress and result in permanent vision loss.

A primary care physician, optometrist, or emergency room physician will perform the first evaluation. Depending on the condition, a visit to an ophthalmologist (eye doctor) for serious conditions may still be needed. 

How is the cause of red eyes diagnosed?

Because there are so many causes of red eye, healthcare providers follow a series of guidelines to diagnose the cause. 

When seeing a healthcare provider, expect to answer questions such as:

  • Are there other symptoms?

  • Has your vision changed?

  • When did the symptoms start?

  • Have you had previous eye problems? Infections? Dry eye syndrome?

  • What is your occupation?

  • What were you doing before the eye problems started?

  • What prescription medications are you taking?

After looking at the eye and taking a medical history, the healthcare provider will typically check your vision to confirm no vision loss. This may involve reading an eye chart, checking peripheral vision, and seeing if you can follow a light with your eyes. 

After this, the clinician may apply a fluorescein dye to the eye's surface and then look at the eye under a special blue light. Scratches, tears, injuries, foreign objects, ultraviolet damage, or herpes infections on the eye’s surface will show up under the light. The inner eyelids may also be examined. The examiner will then test eye pressure with a tonometer to identify vision-threatening glaucoma. The eye may also be examined by a slit lamp device or a fundoscope to look for problems inside the eye. 

Are red eyes contagious? 

Infections of the eye’s surface are contagious, particularly viral infections. Herpes infections of the cornea are not, but the infection needs to be treated to keep it from spreading to other parts of the body.

The Centers for Disease Control and Prevention (CDC) have a few recommendations to prevent the spread of viral and bacterial conjunctivitis:

  • Wash your hands regularly or use hand sanitizer

  • Wash your hands after applying eye drops

  • Avoid touching your eyes or eyelids

  • Avoid contact lenses until a healthcare provider says it’s okay

  • Always clean any fluid or discharge that comes from the infected eye with a cotton ball or disposable wipe—then wash your hands

  • Regularly wash pillowcases and blankets that come in contact with your face

  • Do not share personal items

  • Do not use swimming pools

  • Try to avoid touching other people or objects they use—one study found that almost half of the people with viral conjunctivitis had the virus on their hands

How long do red eyes last?

Red eyes last as long as something in the eye is causing inflammation: 

  • Temporary eye irritation from dust, smoke, or eye rubbing usually resolves without treatment very shortly after the irritant is gone

  • Scratches or other minor injuries may take a few days to improve unless they’re aggravated by rubbing or contact lenses

  • Red eye due to allergic reactions typically improves rapidly with antihistamines

  • Bacterial infections typically resolve with treatment in seven to 10 days

  • Viral infections (except herpes) clear up in a few days

  • Other causes may require more time to improve

How to stop red eyes

Many cases of red eyes resolve on their own without treatment. This includes red eye due to irritation, allergies, and some infections. Other causes of red eyes will require treatment ranging from topical eye medications to emergency surgery.

  • Allergic conjunctivitis can usually be treated by avoiding allergens and using over-the-counter oral or ophthalmic antihistamines, but a healthcare provider can prescribe prescription antihistamine eye drops or, rarely, corticosteroid eye drops in more recalcitrant cases

  • Bacterial conjunctivitis is usually treated with antibiotic eye drops

  • Viral conjunctivitis is typically caused by the cold virus (adenovirus), so treatments focus on easing symptoms

  • Herpes infections are treated with antiviral medications

  • A corneal ulcer is typically treated with appropriate antimicrobial eye drops and frequent follow-up visits, but a corneal transplant may be needed in the worst cases

  • Eye injuries are usually treated with antibiotic drops to help prevent infection

  • Red eye due to autoimmune conditions is typically treated with corticosteroid eye drops

  • Bacterial infections within the eye are treated with oral antibiotics

  • Angle-closure glaucoma is treated with eye drop medications that reduce eye pressure or with emergency eye surgery

RELATED: Pink eye treatments and medications

Living with red eyes 

Recurrent problems with red eyes are usually a sign of allergies, irritants in the air, or repeated exposure to infections. These recurrences can often be prevented:

  • Wash your hands regularly

  • Avoid allergens such as pollen or pet dander

  • Avoid dust, smoke, and chemical fumes—wear protective goggles if you can’t

  • Get an air purifier for your home or office

  • Use a humidifier to prevent dryness

  • Take computer screen breaks regularly

  • Stop smoking

  • Avoid rubbing your eyes

  • Avoid chlorinated water

  • Either avoid eye makeup or remove it regularly using safe washes

  • Don’t wear contact lenses for long periods

  • Clean your contact lenses regularly

Most importantly, take care of your eyes

While many people take good care of themselves, it’s easy to ignore eye health. However, if there’s one thing you don’t want to lose, it’s your eyesight. The best way to treat eye problems like red eyes is to prevent them through good eye care. Here are a few guidelines from the CDC: 

  • Get regular eye exams even if you don’t need glasses or contact lenses

  • Eat a healthy diet

  • Lose weight and maintain a healthy weight

  • Quit smoking or never start

  • Wear sunglasses when outside in the sun to protect the eyes from UV rays

  • Wear safety glasses or goggles when playing sports, at work, or engaging in activities around the house that may cause eye injury 

  • Clean your hands regularly 

RELATED: Eye health 101: how to protect vision and keep your eyes healthy

FAQs about the causes of red eyes

Can high blood pressure cause red eyes?

Some medical conditions, such as high blood pressure or persistently high blood sugar, can cause blood vessels near the eye’s surface to burst, known as subconjunctival hemorrhage. It can look bad when this happens, but it is not a health threat and typically resolves without treatment in two or three weeks. The real worry is the damage that hypertension and diabetes do to the retina's fragile, tiny blood vessels. Over time, this damage can lead to permanent vision loss.

What deficiency causes red eyes?

Vitamin deficiencies can affect the eyes and sometimes result in red eyes. Vitamin A or vitamin B12 deficiency, for instance, can cause dry eye. Without lubricating fluids, the eye's surface is vulnerable to irritation, scratches, and redness. Other vitamin deficiencies weaken blood vessels, such as vitamin C deficiency. One possible sign of a vitamin C deficiency is a blood vessel rupturing near the eye's surface (subconjunctival hemorrhage), causing red eye bleeding and inflammation.

Can high blood sugar cause red eyes?

Like hypertension, diabetes can damage blood vessels throughout the body. In older adults, it is a primary risk factor for subconjunctival hemorrhage. More importantly, uncontrolled high blood sugar over time ruins the blood vessels in the retina, causing progressive and permanent vision loss.

What’s next? Additional resources for people with red eyes

Test and diagnostics

Treatments

Scientific studies and clinical trials

Medically reviewed by Leslie Greenberg, MD
Board-Certified Family Physician

Leslie Greenberg, MD, is a board-certified practicing family physician with more than 25 years of doctoring experience. She was a psychology major at Northwestern University near Chicago, then graduated with an MD from the University of Nevada School of Medicine. She completed her family medicine residency at St. Joseph Hospital in Wichita, Kansas. She has trained more than 350 family medicine resident-physicians, been in private practice, and delivered babies for 22 years.

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