what causes red eyes

Eye redness happens when the tiny blood vessels on the white of your eye get irritated, swollen, or dilated.

Quick Scoop: What causes red eyes?

Think of “red eyes” less as a single problem and more as a symptom with lots of possible triggers.

1. Super common, usually mild causes

• Allergies (pollen, dust, pet dander, makeup, contact lens solution) can inflame the eye surface and make it itchy, watery, and red.

• Dry eyes from screens, air‑conditioning, low blinking, or aging can make the surface rough and inflamed, leading to redness and burning.

• Irritants like smoke, pollution, chlorine in pools, or strong fumes can directly irritate the eye surface.

• Lack of sleep or eye strain (long hours on a computer or phone) can dilate blood vessels and make eyes look bloodshot.

• Contact lens over‑wear (sleeping in them, not cleaning them well, wearing them too long) can dry and irritate the eye or even cause infection.

2. Infections and inflammation

• Conjunctivitis (“pink eye”) is inflammation of the thin membrane over the white of the eye; it can be viral, bacterial, or allergic and often causes redness, discharge, and crusting.

• Keratitis or corneal ulcers (infection or injury of the clear front surface of the eye) cause intense pain, light sensitivity, tearing, and redness; these are emergencies.

• Uveitis (inflammation inside the eye) can cause deep aching pain, blurred vision, and a very red eye, sometimes linked to autoimmune disease or infections.

• Eyelid problems like blepharitis (inflamed eyelid margins) can make the eye surface red and gritty.

3. Injury and burst blood vessels

• Scratches, foreign bodies (dust, metal, sand), or chemical splashes can directly injure the eye and make it red, painful, and watery.

• A subconjunctival hemorrhage (a small blood vessel breaking on the eye’s surface) can make part of the white turn bright red; it looks scary but is often painless and usually harmless.

4. More serious eye diseases

• Acute glaucoma (sudden high eye pressure) can cause a red, very painful eye with blurred vision, halos around lights, and nausea; this is an emergency.

• Severe infections inside the eye (endophthalmitis, cellulitis around the eye) can cause marked redness, swelling, and vision loss and need urgent care.

• Less common causes include certain cancers (like eye lymphoma or retinoblastoma), shingles affecting the eye, and other systemic diseases.

5. Lifestyle and “everyday” factors

• Alcohol or cannabis use can dilate eye blood vessels and make them look bloodshot.

• Strong sun or UV exposure (skiing, beaches, tanning beds without eye protection) can cause photokeratitis, a kind of “sunburn” of the eye, with redness and pain.

• Very dry environments (planes, heated offices, deserts) can worsen dryness and redness.

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<table>
  <tr>
    <th>Category</th>
    <th>Examples</th>
    <th>Typical clues</th>
  </tr>
  <tr>
    <td>Allergic / irritant</td>
    <td>Allergies, smoke, chlorine, fumes [web:1][web:7][web:9]</td>
    <td>Itchy, watery, both eyes, often seasonal or exposure-related</td>
  </tr>
  <tr>
    <td>Dryness / strain</td>
    <td>Dry eye, long screen time, contact lenses [web:5][web:9]</td>
    <td>Burning, gritty feeling, worse later in the day</td>
  </tr>
  <tr>
    <td>Infections</td>
    <td>Conjunctivitis, keratitis, corneal ulcer [web:1][web:3]</td>
    <td>Redness with discharge, pain, light sensitivity, sometimes contagious</td>
  </tr>
  <tr>
    <td>Injury / trauma</td>
    <td>Scratch, foreign body, chemical splash [web:1][web:7]</td>
    <td>Sudden pain, tearing, history of accident or exposure</td>
  </tr>
  <tr>
    <td>Blood vessel issues</td>
    <td>Subconjunctival hemorrhage [web:1][web:7]</td>
    <td>Bright red patch on white of eye, usually painless</td>
  </tr>
  <tr>
    <td>Serious eye disease</td>
    <td>Glaucoma, uveitis, endophthalmitis [web:1][web:3][web:5]</td>
    <td>Severe pain, blurred vision, halos, often needs urgent care</td>
  </tr>
  <tr>
    <td>Lifestyle factors</td>
    <td>Alcohol, cannabis, sun/UV, dry environments [web:3][web:4][web:9]</td>
    <td>Bloodshot appearance after use or exposure, usually mild</td>
  </tr>
</table>

When to see a doctor urgently

You should get urgent medical or eye‑specialist care if red eye comes with:

• Significant pain, sudden vision changes, or seeing halos around lights.

• Recent eye injury, chemical exposure, or something stuck in the eye.

• Severe light sensitivity, nausea, or vomiting with a red eye.

• Redness in a person who wears contact lenses and has pain or blurred vision.

Information gathered from public forums or data available on the internet and portrayed here.