Red eyes are probably the single most common thing people walk into an optical store wanting help with. Someone pulls their lower lid down, leans toward me across the counter, and asks: "Does this look bad?" As a licensed optician, I have seen hundreds of red eyes, and the causes range from "you rubbed your eye too hard" to "you need to see a doctor today." Understanding red eyes causes starts with knowing that redness is a symptom, not a diagnosis. Your eyes turn red when the tiny blood vessels on the surface of your eye (the conjunctiva and sclera) dilate or become inflamed. The underlying reason for that dilation is what matters.
Here is what I have learned from years of working behind the dispensing counter. I cannot diagnose you. That is your optometrist's job. But I can help you understand the most common reasons eyes get red, which ones are harmless, and which ones mean you should stop reading this article and call your eye doctor.
The Most Common Red Eye Causes, Ranked by How Often I See Them
Not all redness is created equal. Some causes are so common that I could spot them from across the store. Others are rare but serious. Here is a breakdown of what I encounter most often.
| Cause | How Common | Severity | Main Symptom Besides Redness |
|---|---|---|---|
| Dry eye disease | Very common | Mild-moderate | Gritty, burning sensation |
| Digital eye strain | Very common | Mild | Tired, aching eyes after screens |
| Allergic conjunctivitis | Very common (seasonal) | Mild-moderate | Intense itching, both eyes |
| Contact lens irritation | Common | Mild-serious | Discomfort with lenses in |
| Viral conjunctivitis (pink eye) | Common | Moderate | Watery discharge, often with cold |
| Bacterial conjunctivitis | Moderate | Moderate | Thick yellow-green discharge |
| Subconjunctival hemorrhage | Moderate | Looks scary, usually harmless | Bright red patch, no pain |
| Corneal abrasion | Less common | Moderate-serious | Sharp pain, tearing, light sensitivity |
| Uveitis/iritis | Uncommon | Serious | Deep aching pain, light sensitivity |
| Acute angle-closure glaucoma | Rare | Emergency | Severe pain, halos, nausea |
Most red eyes I see fall into the top three categories. The person has been staring at a computer for eight hours, their allergies are acting up, or they have chronic dry eye they have been ignoring. Those are manageable. The bottom three on this list are a different story entirely.
Dry Eyes: The Number One Reason People Have Red Eyes
If I had to guess the cause of someone's red eyes without any other information, I would say dry eye disease every time. It is that common. The Canadian Association of Optometrists estimates that dry eye affects roughly 30% of Canadians, and that number climbs higher in our dry prairie winters.
Your tear film has three layers: an oily outer layer, a watery middle layer, and a mucin layer against the eye surface. When any of these layers breaks down, your tears evaporate too quickly, the eye surface dries out, and irritation triggers blood vessel dilation. That is the redness you see.
Common dry eye triggers I hear about daily: forced-air heating, air conditioning, ceiling fans, long drives with the heat blasting, and (the big one) screen time. When you stare at a screen, your blink rate drops by as much as 66%. Fewer blinks means fewer chances for your tear film to refresh itself.
Preservative-free artificial tears are your first line of defense. Brands like Systane Ultra, Refresh Optive, and Hylo are all solid options. If you need drops more than four times a day, preservative-free single-dose vials are the way to go. The preservatives in bottled drops can cause their own irritation with frequent use.
Allergies vs. Infection: How to Tell the Difference
This is the question patients struggle with most. Both allergies and infections make your eyes red, watery, and uncomfortable. But the treatment for each is completely different, and using the wrong one wastes your time (and money).
The biggest clue is itching. Allergic conjunctivitis itches intensely. Both eyes are almost always affected, and you will often have other allergy symptoms like sneezing or a runny nose. The discharge is watery and clear.
Bacterial infections produce thick, coloured discharge. Your eyelids may crust shut overnight. It often starts in one eye and spreads to the other. Itching is mild or absent. Viral infections sit somewhere in between, with watery discharge and mild discomfort, often following a cold.
Over-the-counter antihistamine eye drops like Pataday (olopatadine) work well for allergies. For bacterial infections, you need antibiotic drops. The catch is that most pink eye is actually viral, and antibiotics do nothing for viruses. Your optometrist can tell the difference in a few minutes.
Key takeaway: If both eyes itch intensely and you are sneezing, it is probably allergies. If one eye has thick, coloured discharge and your lids crust shut, it is probably bacterial. If you are not sure, see your optometrist rather than guessing at the pharmacy.
Subconjunctival Hemorrhage: The Red Eye That Looks Terrifying but Usually Is Not
Every few weeks, someone walks into the store looking panicked because there is a solid red patch on the white of their eye. No pain, no vision change, just a bright crimson blotch that looks deeply alarming. This is a subconjunctival hemorrhage, which is a fancy way of saying a small blood vessel popped under the surface.
Think of it like a bruise on your eye. It happens from coughing, sneezing, straining, rubbing your eyes, or sometimes for no obvious reason at all. Blood thinners like aspirin or warfarin make them more likely.
The blood looks dramatic, but it absorbs on its own over one to three weeks. There is no treatment needed. No drops will speed it up. The only time a subconjunctival hemorrhage warrants concern is if it keeps happening repeatedly (get your blood pressure checked) or if it followed trauma to the eye (see a doctor).
When Red Eyes Are an Emergency
Most red eyes are annoying but not dangerous. However, certain combinations of symptoms signal a genuine emergency. I want to be clear about the difference, because the serious causes can lead to permanent vision loss if not treated quickly.
| Symptom Combination | Possible Cause | What to Do |
|---|---|---|
| Red eye + severe pain + halos around lights + nausea | Acute angle-closure glaucoma | Emergency room immediately |
| Red eye + deep ache + extreme light sensitivity | Uveitis / iritis | Urgent eye care same day |
| Red eye + white spot on cornea + pain | Corneal ulcer | Urgent eye care same day |
| Red eye after chemical splash | Chemical burn | Flush with water 15-20 min, then ER |
| Red eye after blunt trauma + vision change | Hyphema / globe injury | Emergency room immediately |
| Red eye + sudden vision loss, no pain | Possible vascular event | Emergency room immediately |
Acute angle-closure glaucoma is the one that worries eye care professionals the most. The pressure inside the eye spikes suddenly, causing severe pain, headache, nausea, and halos around lights. Without treatment within hours, it can cause permanent optic nerve damage. If you have these symptoms together, do not wait for a morning appointment. Go to the ER.
Corneal ulcers are particularly common in contact lens wearers who sleep in their lenses or use them past their replacement schedule. A white spot on the cornea with surrounding redness and pain is the hallmark. This needs prescription antibiotic drops urgently, not over-the-counter treatment.
OTC Drops for Red Eyes: What Works, What Doesn't, and What Makes Things Worse
The eye care aisle at the pharmacy can be overwhelming. There are dozens of products, and many of them are marketing solutions to problems they cannot actually solve. Here is a straightforward comparison of what is available.
| Drop Type | Examples | What It Does | Watch Out For |
|---|---|---|---|
| Artificial tears | Systane, Refresh, Hylo | Lubricates, soothes dryness | Choose preservative-free for frequent use |
| Redness relievers | Visine, Clear Eyes | Constricts blood vessels temporarily | Rebound redness with regular use |
| Antihistamine drops | Pataday, Alaway, Zaditor | Blocks histamine for allergy relief | Only works for allergic redness |
| Antibiotic drops (OTC) | Polysporin Eye Drops | Kills bacteria | Only for bacterial infections, not viruses |
| Lumify | Lumify (brimonidine) | Reduces redness without strong rebound | Treats the look, not the cause |
The most important thing on this list is the rebound redness problem with traditional redness-relief drops. Products containing naphazoline or tetrahydrozoline (like original Visine and Clear Eyes) work by constricting the blood vessels on your eye surface. The redness fades for a few hours, but when the effect wears off, the vessels dilate even more than before. Over time, you become dependent on the drops just to look normal. I have seen people using Visine four to six times a day for months, and their eyes are redder than when they started.
Lumify (brimonidine 0.025%) is a newer option that works differently. It targets a specific receptor that reduces redness with less rebound effect. It is a better choice if you occasionally want your eyes to look less red, but it still does not address the underlying cause.
My honest advice: skip the redness-relief drops entirely. Figure out why your eyes are red and treat that instead. Artificial tears for dryness, antihistamine drops for allergies, and a professional diagnosis for anything else.
Red Eyes From Contact Lenses
Contact lens wearers deal with red eyes more than almost anyone else. The lens sits on your cornea all day, reducing oxygen flow, trapping debris, and creating a surface that bacteria love. Even well-fitted, properly maintained lenses can cause occasional redness.
The rule is simple: if your eyes are red and you wear contacts, take them out. Switch to your backup glasses and see if the redness clears within 24 hours. If it does, the lenses were likely the problem. If redness persists, worsens, or you develop pain, discharge, or light sensitivity, see your optometrist promptly. A corneal infection caught early is treatable. One caught late can scar the cornea permanently.
The most dangerous habit I see is sleeping in contacts that are not approved for overnight wear. This reduces oxygen to the cornea by up to 80% and dramatically increases the risk of bacterial keratitis. Even lenses approved for extended wear carry higher infection risk when slept in. I tell every contact lens patient the same thing: take them out before bed, every night, no exceptions.
When to See Your Optometrist vs. When to Wait It Out
Not every red eye needs a professional visit. Mild redness from a late night, a windy day, or a few too many hours at the computer will resolve on its own with some artificial tears and rest. But there are clear lines where waiting stops being reasonable.
See your optometrist if:
- Redness lasts more than 3 days despite artificial tears
- There is discharge (especially thick or coloured)
- You have pain beyond mild irritation
- Your vision is affected in any way
- Light sensitivity makes it hard to keep your eye open
- You wear contact lenses and redness does not improve after removing them for 24 hours
- Redness keeps coming back
The Canadian Association of Optometrists recommends professional assessment for any red eye that does not resolve quickly, and I agree. A thorough eye exam takes 15 to 20 minutes and can catch things you would never identify on your own. Many serious eye conditions start with redness as the only symptom.
Frequently Asked Questions
Why are my eyes red every morning?
Morning redness is usually caused by dry eyes overnight, incomplete eyelid closure during sleep (a condition called nocturnal lagophthalmos), or dust mite allergies from your bedding. Sleeping with a fan blowing directly on your face is another common culprit. Try preservative-free artificial tears before bed and see if it improves. If the redness is there every single morning, ask your optometrist to evaluate for chronic dry eye disease or incomplete lid closure.
Can screen time cause red eyes?
Yes, and it is one of the most common causes I see. When you focus on a screen, your blink rate drops by up to 66%. Fewer blinks means your tear film dries out faster, leading to irritation and redness. This is called digital eye strain or computer vision syndrome. The 20-20-20 rule helps: every 20 minutes, look at something 20 feet away for 20 seconds. Lubricating drops throughout the day also make a difference.
Are red eyes a sign of high blood pressure?
Chronic high blood pressure can cause changes inside the eye that your optometrist can detect during a dilated exam, but everyday surface redness is rarely caused by blood pressure alone. A subconjunctival hemorrhage (a bright red patch) can occasionally follow a blood pressure spike, though most are harmless and unrelated. If you get frequent subconjunctival hemorrhages, have your blood pressure checked. It is a reasonable precaution.
Should I use eye drops for red eyes?
It depends entirely on the cause. Preservative-free artificial tears are safe for most mild redness from dryness or irritation. Redness-relief drops like Visine contain vasoconstrictors that temporarily shrink blood vessels, but regular use causes rebound redness. Your eyes end up redder than before. For allergic redness, antihistamine drops work well. For anything involving pain, discharge, or vision changes, skip the drugstore and see your eye doctor.
When should I go to the ER for red eyes?
Go to the emergency room if your red eye comes with sudden vision loss or significant blurring, severe pain (not just mild irritation), a chemical splash, a foreign object you cannot flush out, or light sensitivity so intense you cannot open your eye. Also go if you had recent eye surgery and develop new redness. These can indicate conditions like acute angle-closure glaucoma, corneal ulcer, or uveitis that require immediate treatment to prevent permanent damage.
Can contact lenses cause red eyes?
Absolutely, and they are one of the most common causes I see. Overwearing lenses, poor hygiene, sleeping in contacts, old or damaged lenses, and sensitivity to lens solutions all cause redness. If your eyes are red and you wear contacts, remove them and switch to glasses. If the redness does not improve within 24 hours without lenses, see your optometrist. You may have a corneal abrasion or early infection that needs professional care.
Why is only one eye red?
Single-eye redness is common with subconjunctival hemorrhage (a popped blood vessel), bacterial conjunctivitis (which often starts in one eye), foreign bodies or corneal scratches, and styes. It can also indicate more serious conditions like iritis or acute glaucoma, especially if accompanied by pain and vision changes. One red eye that persists for more than a day or two, or that comes with pain, is worth an eye exam.
This article is for informational purposes only and does not constitute medical advice. Always consult your optometrist, ophthalmologist, or family doctor for diagnosis and treatment of eye conditions.