Dogs produce tears, but not for the same reasons you do. Their tear glands keep their eyes lubricated and healthy, and tears flow constantly as a baseline function. When you see your dog with watery eyes, the cause is almost always physical, not emotional. That said, one recent study has complicated this picture in a surprising way.
How Dog Tear Glands Work
Dogs have a lacrimal system similar to humans. About two-thirds of the watery layer of their tears comes from the main tear gland, with the rest produced by a gland in their third eyelid (a membrane humans don’t have). These tears wash over the surface of the eye and then drain through small openings into the nasal cavity or mouth. This process runs continuously to protect the cornea from drying out, flush away debris, and deliver oxygen and nutrients to the eye’s surface.
The chemical makeup of dog tears differs from human tears. Dog tears contain less total protein but higher concentrations of cholesterol and urea compared to human tears. In humans, emotional tears have a distinct chemical profile from the basal tears that simply keep eyes moist. No equivalent distinction has been found in dogs.
How Dogs Express Distress
Dogs communicate sadness, pain, and anxiety through sounds and body language rather than tears. Puppies cry vocally from birth, producing high-pitched whines and whimpers that range widely in frequency. As dogs age, these vocalizations drop in pitch but remain a core part of how they signal distress.
When a dog is upset, you’ll typically see a combination of physical signals: ears flattened back, lowered tail and head, a crouched body posture, and sometimes submissive behaviors like rolling over. Dogs even respond to the distress calls of others this way. When dogs hear a baby crying, their stress hormone levels rise and they display these same submissive postures, suggesting they recognize and react to emotional distress through sound, not tears.
The 2022 Study That Surprised Researchers
A 2022 study from Azabu University in Japan found something no one had documented before in a nonhuman animal. Researchers measured tear volume in dogs before and after reunions with their owners using a standardized test. Dogs produced significantly more tears when reunited with their owners after a period of separation. Crucially, the same increase did not happen when dogs were reunited with familiar people who weren’t their owners.
The researchers then applied an oxytocin solution (oxytocin is a hormone linked to bonding and attachment) directly to dogs’ eyes and found it increased tear volume, suggesting oxytocin may be the mechanism behind the reunion response. In a follow-up experiment, human participants rated photos of dogs with visible tears as more endearing than photos without, which hints at an evolutionary angle: teary-eyed dogs may trigger a stronger caregiving response in people.
This study made headlines, but the scientific community remains split. The finding is preliminary and has not been replicated. Many researchers still hold that producing emotional tears is a uniquely human behavior. The increase in tear volume during reunions could reflect general arousal or excitement rather than a sadness-like emotional state. For now, it’s a fascinating data point, not a settled answer.
Medical Reasons for Watery Eyes
If your dog’s eyes are visibly wet or tearing, the explanation is far more likely to be medical than emotional. The most common causes fall into two categories: the eyes are producing too many tears (usually a reflex response to irritation) or tears aren’t draining properly.
Reflex tearing happens when something irritates the eye. Allergies, dust, foreign objects, scratches on the cornea, and infections all trigger the tear glands to ramp up production. Blocked or narrow tear ducts prevent normal drainage, so tears overflow onto the face even when production is normal. Some dogs are born with underdeveloped drainage channels, making this a lifelong issue.
The color and consistency of the discharge tells you a lot. Clear, watery discharge often points to allergies or minor irritation. Yellow or green discharge suggests a bacterial infection. If only one eye is affected, infection or a localized injury is more likely. Allergies tend to affect both eyes since they’re a whole-body response. Redness, swelling around the eyelids, squinting, pawing at the face, or sensitivity to light all warrant a veterinary visit, ideally within the first 24 hours.
Why Some Breeds Tear More Than Others
Flat-faced breeds like Pugs, English Bulldogs, Shih Tzus, and Lhasa Apsos are especially prone to visible tearing and tear staining. Their shortened skulls and compressed facial structures create a cascade of eye problems. The shape of their eye sockets leaves more of the eye exposed, which means less protection from the eyelids and more surface area vulnerable to drying and irritation.
These breeds are overrepresented in cases of dry eye (which paradoxically can cause excess tearing as the eye tries to compensate), corneal ulcers, eyelid abnormalities where lashes or skin folds rub against the eye, and prolapse of the third eyelid gland. A study reviewing nearly 1,000 cases of brachycephalic dogs at referral hospitals found these conditions were consistently linked to skull shape. If you have a flat-faced breed and notice persistent tear staining or wetness around the eyes, it’s worth having their tear production and drainage evaluated rather than assuming it’s just how they look.
What Watery Eyes Actually Mean
When your dog looks up at you with glistening eyes, it’s natural to read that as emotion. Dogs are remarkably attuned to human feelings, and we’re wired to interpret their expressions through a human lens. But the tears themselves are almost certainly doing what tears are designed to do in dogs: protecting the eye.
That doesn’t diminish what your dog is feeling. Dogs experience joy, grief, anxiety, and attachment in ways that show up clearly in their behavior, brain activity, and hormone levels. They just express those feelings through their voice, body, and actions rather than through their tear ducts. If your dog’s eyes are consistently watery, the most useful thing you can do is look at the discharge itself, whether one or both eyes are affected, and whether your dog seems bothered by it. Those details point toward a cause that can actually be addressed.