14 Common Causes of Red Eyes

2. Sun Exposure

Sun exposure makes your eyes look red when strong light irritates the surface of the eye. Bright sunlight dries the eye and widens small blood vessels, which makes the white part of your eye appear pink or red. You may notice redness after long hours outdoors, especially near water, sand, or snow. These surfaces reflect light and increase exposure. Wind often makes the problem worse by drying your eyes even more.

Sun exposure can also cause a mild burn on the eye’s surface. This may lead to soreness, a gritty feeling, or discomfort in bright light. Vision can become slightly blurred for a short time, then clear as the eye settles. Other signs linked to sun‑related eye redness include watery eyes and a dry or scratchy sensation. Repeated exposure without eye protection raises the risk of ongoing eye irritation. Over time, the surface of the eye may stay dry or inflamed more often, and redness becomes easier to trigger, even with brief time outdoors.

3. Dust

Dust irritates your eyes when tiny particles land on the surface of the eye. These particles scratch and dry the outer layer, which leads to redness and a gritty feeling. Your eyes react fast to protect themselves.

You may notice red or bloodshot eyes soon after dust exposure. Other common signs include itching, burning, and watery eyes. Though your vision may stay clear, blinking can feel uncomfortable. Dust often triggers a mild form of eye inflammation. This reaction is not an infection and does not spread from person to person. The redness comes from swollen blood vessels on the white part of your eye.

Common dust sources include household dust, soil, sand, and fine debris in the air. Outdoor wind, indoor cleaning, and dry air can raise dust levels. Work sites and traffic areas often increase exposure. Dust-related red eyes may be similar to pink eye, with the cause being the key difference. Dust irritation starts after exposure and often affects both eyes at the same time, without thick discharge.

4. Allergies

Allergies cause red eyes when your immune system reacts to things like pollen, dust, pet dander, or mold. When these triggers reach your eyes, the thin clear layer on the surface becomes irritated and blood vessels swell, which makes the white of your eye look red.

You may notice itching, burning, or a gritty feeling. Your eyes can water a lot, and the eyelids may look puffy, especially after sleep. Both eyes usually turn red at the same time, which helps separate allergies from other causes.

Allergy-related redness can change with the seasons. Tree and grass pollen tend to cause problems in spring and summer, while dust and pet dander can bother you all year. Windy and dry days often make symptoms worse because allergens stay in the air longer. Other allergy signs often appear along with red eyes. You might also have a runny nose, sneezing, or an itchy throat. These body-wide clues point to allergies rather than infection or injury.

5. Colds

Colds make your eyes look red and tired. You get a cold from a virus that affects your nose and throat, and the same virus can also irritate your eyes. When you have a cold, your body sends more blood to fight the infection, which causes the small blood vessels in your eyes to swell. As a result, the white part of your eye may turn pink or red.

A cold often causes a runny or stuffy nose. When your nose swells, it can block normal tear drainage. Tears then build up and spill over, which can leave your eyes watery and red. You may also touch or rub your eyes more when you feel sick, and this spreads germs from your hands to your eyes and makes redness worse.

Colds can sometimes lead to viral eye infections which spread easily and may affect one or both eyes. They often clear as your cold improves. Red eyes from a cold usually improve within several days as your body fights off the virus and nasal swelling goes down.

6. Infections

Eye infections cause red eyes because germs irritate the surface of your eye or eyelid. These germs include viruses, bacteria, and fungi. You may notice redness in one eye or both, along with discomfort that ranges from mild to strong.

Conjunctivitis, often called pink eye, is one of the most common infections. Viruses and bacteria can cause it, and both types spread easily between people. Your eye may look pink or red, feel itchy or gritty, and produce watery or thick discharge.

Bacterial infections can also affect the eyelids and nearby skin. A stye appears as a tender bump on the eyelid when bacteria block an oil gland. Blepharitis causes red eyes when bacteria lead to swollen, crusty eyelids that irritate the eye surface.

Some infections affect the clear front layer of your eye, called the cornea. Keratitis causes redness, pain, and blurry vision when bacteria, fungi, or parasites invade this area. Contact lens use raises this risk because germs can stick to the lens.

7. Measles

Measles is a viral illness that causes red, watery eyes along with other body symptoms. You may notice eye redness before the skin rash appears. The virus spreads through the air when an infected person coughs or sneezes.

Your eyes look red and feel sore because the virus causes eye swelling and irritation. You may also feel light sensitivity, which can make bright rooms uncomfortable. Tearing often increases, and your eyes may look glossy or inflamed.

Red eyes from measles usually do not happen alone. You often have a high fever, cough, and runny nose at the same time. These symptoms often start about one to two weeks after you come in contact with the virus.

A few days later, a red rash often spreads across your body. The rash usually starts on the face and moves downward, with eye redness worsening as the rash spreads.

Measles can lead to serious problems, especially in young children. Eye issues may include infection or swelling that affects vision. These problems can become severe if they do not receive care.

8. Eye Trauma

Eye trauma happens when something hits, scratches, or enters your eye. You may get trauma from sports, work tools, falls, or accidents at home. Even small injuries can make your eye look red.

When the eye gets hurt, tiny blood vessels on the white part of your eye swell or break. This causes redness, watering, and soreness. You may also notice light sensitivity or blurred vision.

Common sources of eye trauma include contact with fingers, toys, or sports balls, exposure to dust, sand, or fine debris, contact lens overuse or poor cleaning, and sharp objects such as paper edges or branches.

Some injuries affect only the surface of the eye, while others reach deeper parts that control vision. A scratch on the cornea feels painful and makes blinking hard while a stronger hit raises eye pressure or causes bleeding inside the eye.

9. Sties

A stye is a small, painful bump that forms on your eyelid, often appearing red and swollen. Bacteria block an oil gland or hair follicle near your eyelashes, especially if you touch your eyes with dirty hands or use old eye makeup. Stress, lack of sleep, and poor lid hygiene can increase your risk of developing sties.

You may notice soreness, tearing, or a gritty feeling in your eye. The lid may feel tender when you blink. Some sties form a yellow tip as pus builds up, which can increase redness around the area.

Warm compresses placed over a closed eyelid help the blocked gland open and drain, which reduces swelling and redness. Squeezing or popping a stye can spread infection and worsen irritation. Avoiding eye makeup and contact lenses supports healing. A healthcare provider may prescribe a topical antibiotic if the infection does not improve.

10. Marijuana Usage

Marijuana use often leads to red eyes because it lowers pressure inside your eyes, which causes small blood vessels on the eye surface to widen. More blood flows through these vessels, and this makes your eyes look red or bloodshot. Redness can appear soon after use and last for several hours, even with occasional use.

Smoke irritates your eyes with heat, tiny particles, and dry air, which reduces moisture on the eye surface. When your eyes dry out, they may look red and feel gritty or tired. Edible forms do not expose your eyes to smoke, but redness can still happen after the active compounds enter your bloodstream.

Marijuana can briefly reduce how much fluid your body holds, which causes your eyes to lose moisture. Dry eyes often appear red and feel uncomfortable. When you blink less while using marijuana, it allows tears to dry faster and makes redness more noticeable, especially in bright or windy settings.

11. Rheumatoid Arthritis

Rheumatoid arthritis is a long-term condition where your immune system attacks your joints and can also affect your eyes. Inflammation inside the eye tissues can make your eyes look bloodshot and feel painful or sensitive to light. You may experience dry eye, episcleritis, scleritis, or uveitis, each causing various degrees of redness, discomfort, and vision changes.

Dry eyes often cause burning, redness, and a gritty feeling. Episcleritis tends to be milder and usually leads to surface redness and discomfort. Scleritis affects deeper eye tissues and can cause intense redness, deep pain, and vision changes. Uveitis involves inflammation inside the eye and may result in redness, pain, and blurred vision.

Some eye problems cause mild symptoms, while others can affect your vision. Red eyes may appear when your joint symptoms flare up. Poor control of joint inflammation can raise the risk of eye problems.

12. Scleritis

Scleritis causes redness because the white part of your eye becomes swollen and irritated, often spreading across a wide area. Inflammation here can feel intense, and you may feel strong eye pain that does not improve with rest. The eye can feel tender to touch, and light may bother you. Some people notice blurry vision or tearing.

This condition often links to immune system problems, where your body attacks healthy tissue by mistake and causes eye swelling. You can have scleritis in one or both eyes, and it may return after treatment.

Doctors diagnose scleritis with a careful eye exam and may order blood tests to check for body-wide inflammation. Treatment focuses on lowering swelling and pain with eye drops or pills from the corticosteroid drug class, nonsteroidal anti-inflammatory drugs, or immune-suppressing drugs for severe cases. Without treatment, scleritis can damage the eye wall and affect vision. Prompt care helps protect your sight and reduces repeat flare-ups.

13. Improper Use of Contacts

Contact lenses can trigger red eyes when you use them in unsafe ways, which causes irritation, redness, dryness, or a gritty feeling. Sleeping in contacts limits oxygen to your eyes, and this leads to swelling and makes blood vessels stand out. Poor cleaning habits allow germs to grow on lenses and cases, which can irritate your eyes and cause infections.

Water exposure from tap water, pools, or lakes can carry tiny organisms that stick to lenses and trigger redness, pain, and blurred vision. Wearing contacts longer than intended can also cause redness, as old or damaged lenses develop rough edges and deposits that scrape the eye surface. A poor fit causes friction with each blink, which leads to visible redness and discomfort.

Early signs often include burning, itching, or light sensitivity. Some people also notice discharge or blurry vision. These symptoms can worsen if the cause continues without correction.

14. Cornea Scratch

A cornea scratch occurs when something scrapes the clear front surface of your eye, which helps you see clearly and shields your eye from dirt and germs. Even a small scratch can make your eye red and very sore. This common eye injury can result from daily activities or accidents.

You may notice sharp pain, a gritty feeling, or the sense that something is stuck in your eye. Your eye may water a lot and feel sensitive to light. Vision can turn blurry for a short time, especially if the scratch sits near the center of the eye.

Common causes include a fingernail, a loose eyelash, or rubbing your eye when dust or sand gets inside. Contact lenses can also raise your risk, especially if they do not fit well or if you wear them too long. Everyday accidents like brushing past a branch or towel can also lead to a scratch.

Irritation and swelling in the eye cause redness after a cornea scratch. The eye reacts fast because this surface has many nerves. Pain often feels strong at first but tends to ease as the surface repairs itself.