Not All Eye Discharge Is Created Equal
Every dog owner has seen those small crusty bits collected in the inner corner of their dog's eyes first thing in the morning. In most cases, this is completely normal — a natural byproduct of the eye's self-cleaning mechanism. But discharge can also be the first visible sign that something is wrong, and knowing how to tell the difference is a genuinely useful skill.
The key factors to consider are the colour, consistency, quantity, and which eye is affected — and whether the discharge is accompanied by any other signs of discomfort or irritation.
Normal Eye Discharge
Healthy dogs produce a small amount of discharge as part of normal eye function. The tear film constantly flushes the ocular surface, carrying away debris, dead cells, and environmental particles. This material collects in the medial canthus — the inner corner of the eye — and dries to form small crusts, often called sleep, rheum, or colloquially, eye boogers.
Normal discharge is typically clear to light brown or rust-coloured, small in quantity, and present primarily after sleep. It should wipe away easily with a damp cotton pad and should not be associated with redness, squinting, or any apparent discomfort.
Some breeds produce more discharge than others as a matter of anatomy rather than disease. Brachycephalic breeds like Pugs, Bulldogs, and Shih Tzus have shallow orbits and prominent eyes that are more exposed to the environment. Breeds with loose lower eyelids, like Basset Hounds and Saint Bernards, tend to accumulate more debris. In these dogs, a slightly greater volume of clear or light discharge can be entirely normal.
Epiphora: When Tears Overflow
Epiphora refers to overflow of tears onto the face, resulting in the dark, reddish-brown staining seen in the fur below the eyes of many light-coated breeds. The discolouration comes from porphyrins — pigments in tears that oxidise when exposed to air and light.
Epiphora can be anatomical, resulting from blocked or underdeveloped nasolacrimal (tear) ducts, shallow orbits, or entropion. It can also be caused by excessive tear production due to allergies, irritation, or chronic low-grade inflammation. In mild cases with no underlying pathology, management focuses on keeping the facial fur clean and dry to prevent secondary skin infections rather than eliminating the staining entirely.
However, if epiphora develops suddenly in a dog that has not previously experienced it, or if it is accompanied by squinting or redness, a veterinary check is warranted to rule out an underlying cause.
Yellow or Green Discharge
Purulent discharge — yellow, yellow-green, or green in colour — signals infection or significant inflammation. The colour indicates the presence of white blood cells responding to a pathogen or irritant. This type of discharge is not normal and warrants veterinary attention.
Common causes include bacterial conjunctivitis, corneal ulceration with secondary infection, foreign bodies, and blocked tear ducts with secondary infection. The discharge may crust heavily, causing the eyelids to stick together, particularly after sleep. It may accumulate faster than it can be wiped away and is often accompanied by redness, swelling of the conjunctiva, and visible discomfort.
Treatment depends on the underlying cause. Bacterial conjunctivitis is typically treated with topical antibiotic eye drops or ointment. Corneal ulcers require more intensive management. A vet will need to examine the eye to determine the root cause before recommending appropriate treatment.
White or Grey Mucous Discharge
A thick, white or greyish discharge that accumulates steadily is often associated with dry eye (keratoconjunctivitis sicca). Without sufficient tear film, the eye compensates by producing mucus, which builds up as a ropy or stringy discharge. The eye may look dull rather than bright, and the dog may blink frequently or appear mildly uncomfortable.
KCS is diagnosed by measuring tear production with a Schirmer tear test — a small strip of paper placed briefly against the lower eyelid. Normal tear production should wet more than 15mm of the strip in one minute. Readings below 10mm are diagnostic for KCS. Treatment involves stimulating tear production with cyclosporine or tacrolimus drops and supplementing with artificial tears.
Blood-Tinged Discharge
Any reddish or blood-tinged discharge from the eye requires prompt veterinary assessment. Causes include trauma, a foreign body, severe inflammation, or in rare cases, bleeding disorders. This is not a wait-and-see situation.
One Eye Versus Both Eyes
The pattern of which eye is affected can provide useful diagnostic clues. Discharge affecting only one eye suggests a localised cause — a foreign body, a unilateral corneal ulcer, a blocked tear duct, or a localised infection. Discharge affecting both eyes simultaneously points more toward a systemic or generalised cause such as allergies, a viral infection, or KCS.
This is not an absolute rule — bilateral conditions can start in one eye and spread, and some localised conditions do affect both eyes — but it is a useful starting point when assessing what you're dealing with.
When to Clean and When to Call the Vet
Routine cleaning of normal discharge is appropriate and beneficial. Use a clean, damp cotton pad to gently wipe away material from the inner corner of the eye, always using a fresh pad for each eye. Never use cotton wool that could leave fibres in the eye, and avoid alcohol-based products or human eye drops unless specifically instructed by your vet.
Contact your vet if you notice any of the following:
- Discharge that is yellow, green, or contains blood
- A sudden increase in discharge volume
- Thick, ropy white or grey discharge building up throughout the day
- Eyelids sticking together
- Discharge accompanied by squinting, redness, or pawing at the eye
- Any cloudiness or change in the appearance of the eye alongside discharge
- Discharge that develops in a dog with no prior history of eye issues
Eye discharge is one of those symptoms that can be entirely benign or a sign of something that needs swift attention. The context — what the discharge looks like, how much there is, how the eye looks overall, and how your dog is behaving — tells you almost everything you need to know about whether this is a morning wipe-down situation or a reason to pick up the phone.