Conjunctivitis is inflammation of the conjunctiva, the thin tissue that lines the inside of your dog’s eyelids and covers the white of the eye. It’s one of the most common eye problems in dogs, and most cases resolve within a few days to two weeks with proper treatment. The causes range from bacterial infections and allergies to foreign objects and structural eyelid problems that some breeds are born with.
What Causes Conjunctivitis in Dogs
The underlying cause often depends on whether one eye or both eyes are affected. When both eyes are red and irritated, the culprit is usually a viral or bacterial infection, an allergic reaction, or environmental irritants like dust, pollen, or smoke. When only one eye is involved, it’s more likely caused by a foreign object (a grass seed or bit of dirt), a blocked tear duct, or dry eye, a condition where the eye doesn’t produce enough tears to stay lubricated.
Allergies are a particularly common trigger. Dogs with seasonal allergies or sensitivities to household chemicals, perfumes, or certain foods can develop recurring bouts of conjunctivitis that flare up alongside other allergy symptoms like itchy skin or sneezing.
Breeds at Higher Risk
Some dogs are structurally predisposed to conjunctivitis because of the way their eyelids are shaped. Entropion, where the eyelid rolls inward against the eye, causes constant irritation. Ectropion, where the lower lid droops and sags outward, exposes the conjunctiva to debris and drying. In dogs with entropion, conjunctivitis is the most common secondary problem, occurring in about 41% of affected animals. Ectropion carries a similar pattern, with conjunctivitis developing in roughly 31% of cases.
The breeds most affected by these eyelid abnormalities include Shar-Peis, Chow Chows, Neapolitan Mastiffs, Clumber Spaniels, Saint Bernards, and English Bulldogs. Shar-Peis top the list by a wide margin, with over 15% developing conformational eyelid problems in a given year. Flat-faced (brachycephalic) breeds like Pugs, Pekingese, and Shih Tzus also have higher odds of eyelid issues because of their skull shape, shallow eye sockets, and prominent eyes. For these breeds, conjunctivitis isn’t just a one-time event. It can be a recurring issue unless the underlying structural problem is corrected surgically.
How to Recognize the Signs
The three hallmark signs are eye discharge, squinting or excessive blinking, and redness or swelling around the eyes. The color and consistency of the discharge can hint at the cause. Clear, watery discharge tends to point toward allergies or mild irritation. Cloudy, yellow, or greenish discharge suggests a bacterial infection. You might also notice your dog pawing at the affected eye or rubbing their face against furniture or carpet to relieve the discomfort.
Swelling of the conjunctiva itself can make the tissue look puffy and almost balloon-like around the eye. In mild cases, you may only see slight redness along the inner lid. In more severe cases, the eye can look nearly swollen shut.
How Vets Diagnose It
A vet will start with a physical examination of the eye and surrounding structures, but several quick tests help narrow down the cause and rule out more serious problems. A tear production test uses a small paper strip placed at the edge of the eye for 60 seconds to measure how much moisture the eye produces. Low readings indicate dry eye, which requires a different treatment approach than infection or allergies.
A fluorescein stain test involves placing a drop of orange dye on the eye’s surface. Under a blue light, the dye highlights any scratches or ulcers on the cornea that might be causing or worsening the irritation. This is especially important if a foreign body is suspected, since a corneal ulcer left untreated can threaten your dog’s vision. If the vet suspects a bacterial infection, they may take a small sample from the eye before staining to identify the specific organism involved.
Treatment and What to Expect
Treatment depends entirely on the cause. Bacterial conjunctivitis is typically treated with antibiotic eye drops or ointment applied two to four times daily. Most antibiotic regimens use a combination of ingredients to cover a broad range of bacteria. You’ll usually apply a thin strip of ointment directly onto the eye or drop a solution into the space between the eye and lower lid. Some formulations also include a mild steroid to reduce inflammation, though these are only used when the vet has confirmed there’s no corneal ulcer, since steroids can make ulcers worse.
Allergic conjunctivitis is managed by reducing exposure to the allergen when possible and using anti-inflammatory eye drops to control symptoms. If your dog has chronic allergies, your vet may recommend ongoing management strategies beyond just eye medication. For dry eye, a specific ointment that stimulates tear production is applied every 12 hours, often as a long-term treatment.
If a structural issue like entropion is the root cause, surgery to reshape the eyelid is the definitive fix. Without it, the conjunctivitis will keep coming back no matter how many rounds of eye drops you go through.
Recovery Timeline
Most cases of conjunctivitis resolve within a few days to about two weeks with appropriate treatment. You should notice improvement, particularly less discharge and squinting, within the first two to three days. If your dog’s eye isn’t looking better after several days of treatment, the original diagnosis may need to be revisited. It’s important to finish the full course of medication even if the eye looks normal before the treatment period ends, since stopping early can allow the infection to return.
Can It Spread to Other Pets or People
Simple bacterial or allergic conjunctivitis in dogs is not a significant risk to humans. Unlike the highly contagious viral pink eye that spreads rapidly among children, most cases of canine conjunctivitis are caused by bacteria or irritants that don’t easily jump to people. That said, basic hygiene still matters. Wash your hands after applying your dog’s eye medication or cleaning discharge from around the eye.
If you have multiple dogs in the household, infectious conjunctivitis can potentially spread between them, particularly if it’s viral. Keeping the affected dog’s bedding and food bowls separate during treatment is a reasonable precaution. One notable exception worth knowing: leptospirosis, a bacterial disease dogs pick up from contaminated water, can cause conjunctivitis as one of its symptoms and is transmissible to humans through contact with an infected dog’s urine. This is a systemic illness with much broader symptoms than eye redness alone, including fever, vomiting, and changes in urination.