Red Eyes: Infection, Allergy or Something Serious?

Medically reviewed by Dr. Santosh Sinha

Author’s perspective: Red eyes are so common that most of us shrug them off. Usually that is fine: tiredness, dust or a mild infection explains most cases. But a small number of red eyes signal something serious that needs care within hours, not days. My aim with this post is not to make anyone anxious. It is to help you recognise the difference between “this can wait and settle” and “this needs a doctor today”.

Why eyes turn red

The white of the eye is covered by a thin layer called the conjunctiva, which contains tiny blood vessels. When the eye is irritated, inflamed or under pressure, these vessels widen and become visible, making the eye look red or pink.

The cause can be on the surface of the eye (most common), or deeper inside the eye (less common, but more serious).

Common, usually less serious causes

1. Infectious conjunctivitis (eye flu)

• Signs: redness, watering, gritty feeling, discharge (watery in viral, thicker in bacterial), crusting on waking.
• Often: starts in one eye and spreads to the other; may come with a cold.
• Vision: usually normal, or slightly blurred by discharge that clears on blinking.
• Pain: mild irritation rather than deep pain.
• Contagious: yes.

2. Allergic conjunctivitis

• Signs: intense itching, watery eyes, puffy lids, both eyes at once.
• Often: comes with sneezing, a runny nose, and exposure to dust, pollen or pets.
• Vision: normal.
• Contagious: no.

3. Dry eyes

• Signs: burning, grittiness, redness that worsens with screen use or heaters, sometimes watery eyes as a reflex.
• Vision: may fluctuate, improves with blinking.
• Contagious: no.

Our post on dry eyes and screen strain covers this in more detail.

4. Pollution and smoke irritation

• Signs: burning, watering and redness after exposure to smoke, smog or firecracker fumes.
• Often: improves after moving to cleaner air and rinsing the face with clean water.

5. Subconjunctival haemorrhage

• Signs: a bright red patch on the white of the eye, often noticed in the mirror, with little or no pain.
• Often: follows coughing, sneezing, straining or rubbing. Usually harmless and fades over one to two weeks, but worth checking if it recurs or if you take blood thinners or have high blood pressure.

Less common but serious causes

These need prompt medical attention.

1. Acute angle-closure glaucoma

• Signs: sudden, severe eye pain, headache, blurred vision, seeing haloes around lights, nausea or vomiting, a red eye, sometimes a hazy cornea.
• Why it matters: eye pressure rises suddenly and can damage the optic nerve within hours.
• Action: this is an emergency. Go to an eye hospital or emergency department immediately.

Note: the more common type of glaucoma (open-angle) usually causes no redness or pain, which is why regular eye check-ups after 40 matter.

2. Uveitis (inflammation inside the eye)

• Signs: redness concentrated around the coloured part of the eye, aching pain, light sensitivity, blurred vision.
• Action: see an eye doctor within a day.

3. Keratitis or corneal ulcer

• Signs: pain, strong light sensitivity, blurred vision, a feeling of something in the eye, sometimes a white spot on the cornea.
• High risk: contact lens wearers, eye injuries (especially with plant matter), and use of steroid drops.
• Action: see an eye doctor urgently.

4. Scleritis

• Signs: deep, boring eye pain that may wake you at night, redness, tenderness.
• Often: linked with autoimmune conditions.
• Action: see an eye doctor promptly.

5. Injury or chemical splash

• Action: for chemicals, rinse the eye with clean running water for at least 15 minutes and go to hospital immediately. For injuries, do not rub; seek urgent care.

Quick guide: red flags that need urgent care

Go to a doctor the same day, or to emergency, if a red eye comes with:

• Moderate to severe eye pain
• Blurred or reduced vision that does not clear with blinking
• Strong sensitivity to light
• Haloes around lights
• Headache with nausea or vomiting
• A white spot on the cornea
• Contact lens use with pain and redness
• Recent injury or chemical exposure

What to tell the doctor

A clear history helps your doctor reach the right diagnosis faster:

• When the redness started, and whether it began suddenly
• Whether it is in one eye or both
• Any pain, and how severe it is on a scale of 1 to 10
• Changes in vision, haloes or light sensitivity
• Any discharge and its colour
• Contact lens use, recent injury or eye surgery
• Any eye drops you have already used, including their names

What you can do at home for mild redness

• Rest your eyes and reduce screen time.
• Use cool compresses for comfort.
• Avoid rubbing.
• Clean any discharge gently with clean, lukewarm water and a fresh cotton pad for each eye.
• Avoid smoke, dust and firecracker fumes.
• Wash hands often if infection is possible.

What not to do

• Do not use steroid eye drops or any drops without a prescription. Steroids can worsen some infections and raise eye pressure.
• Do not put herbal powders, Triphala, capsule contents, honey or home mixtures into your eyes.
• Do not wear contact lenses while your eyes are red.

Frequently asked questions

The bottom line

Most red eyes are caused by infection, allergy, dryness or irritation, and settle with simple care. But red eyes with pain, blurred vision, light sensitivity, haloes or nausea can signal serious conditions like acute glaucoma, uveitis or a corneal ulcer, and need urgent care. When in doubt, get it checked.

Disclaimer: This article is for general information and is not medical advice. Please consult an eye doctor for diagnosis and treatment. This article is written for adults; for children, consult a paediatrician.