SYMPTOM
Excessive tearing
Owners may see a damp patch or a line of wet fur running down from the inner corner of the eye, reddish-brown staining of the fur below the eye, or tears spilling onto the face. It may affect one eye or both. Some animals also squint, hold the eye shut, or rub and paw at it, which are signs that the eye is sore rather than simply overflowing.
Nasolacrimal Duct Obstruction
Tears normally drain from the eye into the nose through a narrow duct, and when this pathway is blocked or tears cannot reach its opening, they overflow onto the face instead. In flat-faced breeds such as Persians, Pugs and Shih Tzus, the duct follows a more sharply angled path, and an inward roll of the lower lid near the nose can cover its opening, making this a common and largely anatomical explanation in these breeds.
Conjunctivitis
Inflammation of the membrane covering the eye and lining the lids increases reflex tear production as the eye responds to the irritation. Viral, bacterial and allergic causes are all recognised in both species, and the tearing is usually accompanied by some redness or mild discharge.
Entropion
Inward rolling of the eyelid margin brings the surrounding hair into continuous contact with the corneal surface, generating ongoing reflex tearing as the eye responds to this irritation. It is particularly recognised in breeds with loose facial skin such as Shar Peis and Chow Chows, and in cats it is less common but does occur, especially where facial conformation is flat.
Glaucoma
A rise in pressure within the eye is painful and stimulates reflex tear production alongside other signs such as a cloudy or enlarged appearance to the eye. It can develop on its own or secondary to other eye disease. In dogs, certain breeds, including Cocker Spaniels and Basset Hounds, carry a recognised predisposition, and most dogs with a sudden rise in pressure lose sight in that eye within hours to days. In cats, glaucoma is mostly secondary to uveitis or tumours inside the eye.
Environmental Irritants and Allergies
Dust, pollen, smoke, or strong household products can trigger reflex tearing in an otherwise healthy eye simply through surface irritation, without any underlying eye disease being present. This tends to affect both eyes evenly and to vary with exposure, easing once the irritant is removed.
Why timing matters
Early observation
Tearing with squinting, a cloudy or red eye, or an eye that looks larger than the other can mean glaucoma or a deep corneal ulcer. Sight can be lost within hours to days of a sudden pressure rise, and a melting ulcer can go from a normal cornea to a perforated eye within 24 hours.
Later presentation
Neither the pressure inside the eye nor the depth of an ulcer can be judged at home: they need a pressure reading and a fluorescein stain test. Tearing that goes on for weeks can also irritate and infect the skin below the eye.
Even, long-standing tearing from both eyes in a flat-faced breed, with no squinting and no change in how the eye looks, is more often anatomical. Sudden tearing in one eye, especially with signs of pain, carries more weight.
Conditions commonly associated
Corneal Ulcers
Reflex tear production increases in response to corneal irritation and injury.
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Uveitis
Watery ocular discharge commonly accompanies uveitis.
Distichiasis
Where the extra lashes rub on the corneal surface, the irritation triggers reflex tearing, which can come and go.
Ectopic Cilia
Direct contact between the errant hair and the corneal surface triggers a strong reflex tearing response.
Ectropion
A sagging lower lid disrupts the normal tear drainage pathway, so tears pool and overflow down the face.
Facial Nerve Paralysis
Without a normal blink the eye surface is poorly protected, and painful corneal ulcers are common, which cause watering. Tear production can also fall, so the affected eye may become dry rather than watery.
Entropion
An inward-rolling eyelid brings hair into contact with the corneal surface, causing ongoing reflex tearing.
Glaucoma
A painful rise in pressure inside the eye stimulates reflex tearing, often with a cloudy or enlarged eye.
Conjunctivitis
Inflammation of the membrane covering the eye increases reflex tear production, usually with some redness or discharge.
When to explore further
When the symptom is persistent or worsening
When tearing starts suddenly in one eye, or comes with squinting, holding the eye shut, pawing at the eye, or a cloudy, red, bulging or enlarged eye
When daily activities or quality of life are affected
When there is uncertainty about the cause
Noting when this symptom occurs, any triggers, and how it changes over time can provide useful information for veterinary discussions.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS