Why Do Dogs Produce Tears
Dogs do produce tears, but their tear system works differently from humans. Dogs have a nasolacrimal duct that drains tears from the eyes into the nasal cavity, which is why crying with visible tears is rare. The main functions are lubrication, debris removal, and maintaining clear vision. According to veterinary ophthalmology research, dogs have a basic tear film with lipid, aqueous, and mucin layers that protect the cornea. When tear production or drainage is disrupted, overflow can cause tears to spill onto the fur. This is often confused with emotional crying, but it is usually a sign of an underlying issue. For more on how animal physiology differs from humans, see the American Kennel Club's guide on dog tear production.
Several common factors can increase tear production or block drainage in dogs. Allergies, dust, smoke, or shampoo residue can irritate the eyes and trigger reflex tearing. Conjunctivitis, corneal ulcers, and eyelash abnormalities such as entropion or distichiasis can also cause excess tears. Blockage of the nasolacrimal duct, called nasolacrimal duct obstruction, prevents normal drainage and leads to tear overflow. Certain brachycephalic breeds like Pugs, Bulldogs, and Shih Tzus are more prone to tear staining because of their facial structure. Breeds such as Poodles and Cocker Spaniels may be more susceptible to primary acquired nasolacrimal duct obstruction. If your dog has persistent tearing, a veterinarian can perform a fluorescein stain test and duct flushing to check for blockages or corneal damage.
What Causes Tear Stains on Dogs
Tear stains are the reddish-brown streaks that appear under a dog's eyes, especially on light-colored fur. They are caused by porphyrins, which are iron-containing molecules produced when the body breaks down red blood cells. Porphyrins are excreted through tears, saliva, and urine, and when they sit on the fur, oxidation turns them a rust color. According to veterinary dermatology studies, the primary cause of excessive staining is chronic tear overflow, often from shallow eye sockets, blocked nasolacrimal ducts, or hair irritation around the eyes. Some research also points to a yeast called Malassezia, which can thrive in the moist environment under the eyes and worsen staining. For more on how tear chemistry affects fur, see VCA Hospitals' article on tear stains in dogs.
Diet and water quality can also influence tear staining. Some dogs react to ingredients like artificial dyes, preservatives, or high-grain fillers, which can increase inflammation and tear production. Hard water with high mineral content may also contribute to staining. Cleaning the area gently with a vet-approved eye wash or saline solution can help reduce buildup. Avoid using hydrogen peroxide or human products near the eyes, as they can cause irritation. Keeping the fur around the eyes trimmed short reduces the surface area where tears collect. If staining is severe or accompanied by redness, swelling, or discharge, a veterinarian should check for infection, allergies, or duct obstruction.
When to See a Vet for Dog Tears
Occasional clear tears are normal, but persistent or colored discharge can signal a problem. Yellow or green mucus often indicates a bacterial infection such as conjunctivitis or keratitis. Squinting, pawing at the eyes, redness, or swelling are signs of pain or irritation that require prompt attention. Corneal ulcers, which can be caused by scratches or foreign objects, may produce excessive tearing and cloudiness. According to veterinary guidelines, untreated ulcers can lead to perforation or permanent vision loss. If your dog has sudden tearing, especially after a fight, outdoor activity, or exposure to chemicals, seek veterinary care immediately. For more on recognizing eye emergencies, see the Merck Veterinary Manual's section on ocular emergencies.
Veterinarians use several tests to diagnose the cause of excessive tearing. The Schirmer tear test measures baseline tear production to rule out dry eye