Dogs produce tears primarily to protect and nourish their eyes, not to cry the way humans do. A thin film of tears coats the surface of your dog’s eyes at all times, keeping them moist, flushing out debris, and delivering oxygen to the cornea. When you notice visible wetness or streaking around your dog’s eyes, it usually means something is causing extra tear production or preventing normal drainage.
How the Tear Film Works
Your dog’s tear film has three layers: a lipid (oily) outer layer, a watery middle layer, and a mucous layer closest to the eye’s surface. Together, these layers maintain a smooth optical surface, supply antimicrobial substances, and deliver oxygen to the cornea, which has no blood vessels of its own. After doing their job, tears drain through the nasolacrimal duct, a small channel that runs from the inner corner of the eye down into the nose. That’s why dogs with healthy tear systems don’t have visible wetness on their faces: the tears are constantly produced and constantly drained.
When either side of that equation tips, tears become visible. Overproduction floods the drainage system faster than it can keep up, while a blocked or narrow duct means even normal tear volume has nowhere to go.
Can Dogs Cry From Emotion?
For a long time, the answer was a flat no. But a 2022 study published in Current Biology found that dogs do produce more tears during emotionally charged moments. Researchers measured tear volume in 18 dogs under normal conditions and then again within the first five minutes of reuniting with their owners after five to seven hours apart. Tear volume increased significantly during the reunions.
The mechanism appears to involve oxytocin, the same hormone linked to bonding in humans. When researchers applied an oxytocin solution directly to dogs’ eyes, tear volume rose in a similar way. Oxytocin levels are already known to spike in dogs during reunions with people, so the connection makes biological sense. In a separate part of the study, human participants rated photos of dogs with visible tears as more emotionally appealing than photos of the same dogs without tears, suggesting the response may have evolved to strengthen the bond between dogs and their owners.
This doesn’t mean your dog sobs when they’re sad. The tear increase is subtle, not the kind of streaming you’d notice across the room. Visible, persistent tearing almost always has a physical cause.
Common Medical Causes of Excess Tearing
The eye’s natural response to irritation is to produce more tears. A long list of conditions can trigger that reflex:
- Conjunctivitis. Bacterial or viral infection of the membrane lining the eyelids. Often accompanied by redness and swelling.
- Allergies. Pollen, dust, mold, and airborne irritants like smoke or strong fragrances can inflame the eye’s surface.
- Corneal ulcers. A scratch or erosion on the clear front surface of the eye. These are painful and can worsen quickly.
- Abnormal eyelashes. Conditions called distichiasis or ectopic cilia cause extra lashes to grow in unusual positions, rubbing against the cornea with every blink.
- Glaucoma. A painful buildup of pressure inside the eye that triggers heavy tearing along with redness and a cloudy appearance.
- Eye injuries. Even a minor poke from a branch or another dog’s paw can cause tearing that lasts hours or days.
In most of these cases, the tearing is your dog’s attempt to flush out the problem. It’s a protective mechanism, but it also signals that something needs attention.
Eyelid Problems That Cause Chronic Tearing
Some dogs deal with tearing their entire lives because of the way their eyelids are shaped. Entropion is a condition where the eyelid rolls inward, pressing the lashes directly against the cornea. It can affect the upper lid, the lower lid, or both, and it can happen in one eye or both. Dogs with entropion typically squint, produce excessive tears, and may be sensitive to bright light. Some rub their faces against furniture or carpet trying to relieve the irritation. In mild cases it’s a minor annoyance, but in severe cases the constant friction creates ulcers and scarring that can permanently affect vision.
Ectropion is the opposite: the lower lid droops outward, exposing the inner surface and making it easier for dust and debris to collect. Both conditions are correctable with surgery, and both are more common in certain breeds.
Why Some Breeds Tear More Than Others
Flat-faced (brachycephalic) breeds like Pugs, Bulldogs, Shih Tzus, and Pekingese are especially prone to visible tearing. Their shallow eye sockets mean the eyes protrude more, exposing a larger surface area to irritants and making it harder for tears to drain efficiently. Their nasolacrimal ducts also tend to be shorter and more curved, which increases the chance of blockages.
Breeds with loose facial skin, like Bloodhounds and Saint Bernards, are more likely to develop ectropion. Breeds with tight, wrinkled skin around the eyes, like Shar-Peis, lean toward entropion. If you own one of these breeds, some degree of tearing may be normal for your dog, but a sudden increase or a change in the color of the discharge is still worth investigating.
What Tear Stains Actually Are
Those reddish-brown streaks beneath a dog’s eyes, especially visible on white or light-colored fur, aren’t dried blood. They’re caused by porphyrins, iron-containing molecules that the body produces as a byproduct of breaking down red blood cells. Porphyrins are excreted through tears, saliva, and urine. When they sit on fur and are exposed to sunlight, they oxidize and turn that distinctive rusty color. The staining itself is cosmetic, not harmful, but heavy or sudden staining can indicate that your dog is producing more tears than usual and may point to an underlying issue.
Signs That Need Prompt Attention
Clear, watery discharge from one or both eyes is often benign, especially in breeds prone to tearing. But certain changes signal something more serious. Thick yellow or green discharge suggests infection. A cloudy or blue-white appearance to the cornea can indicate an ulcer or glaucoma. If your dog keeps one eye firmly closed, refuses to open it, or paws at their face repeatedly, they’re likely in significant pain. A visible depression or bulging area on the cornea’s surface is an emergency: it means the cornea is weakening and could rupture.
Increased swelling around the eye, sudden onset of squinting in a dog that was fine hours ago, or any change in the appearance of the cornea itself all warrant a same-day call to your vet.
Cleaning Your Dog’s Eyes Safely
For routine maintenance, especially if your dog is a breed that tears regularly, you can clean the area around the eyes with a few simple tools. Sterile saline solution is the safest option for flushing out minor irritants like dust. You can also use vet-recommended eye wipes or a clean cloth dampened with water that’s been boiled for at least one minute and then cooled. Wipe gently along the eyelid’s surface, moving toward the ear, and use a fresh cloth or cotton ball for each eye.
Human eye-cleaning products that contain only sterile saline are safe, but avoid anything with additives, and never use alcohol-based products, hydrogen peroxide, or rough materials like cotton swabs near the eye. If your dog isn’t used to having their face handled, start with short sessions in a calm environment. Hold their head gently with one hand without squeezing, reward them with a treat, and gradually build up to longer cleaning sessions over days or weeks. Dogs that learn to tolerate eye cleaning early will be much easier to manage if they ever need medicated drops down the road.