Why Is My Cat's Eye Discharging?
Eye discharge is one of the most common reasons cat owners seek veterinary advice. It can range from a small amount of clear watering to thick, coloured matter that crusts around the eyelid. While occasional mild discharge is perfectly normal — cats do not produce tears in the same way humans do when emotional — persistent or unusual discharge nearly always has an underlying cause that warrants attention.
Understanding what type of discharge your cat has, and how it developed, is the first step towards identifying whether this is something that can be managed at home or whether your cat needs to see a vet promptly. This guide walks through the most common causes, ranked by how frequently they are seen in UK veterinary practice, along with what the discharge itself can tell you.
Most Common Causes of Eye Discharge in Cats
1. Upper Respiratory Infections — Feline Herpesvirus and Calicivirus
By far the most frequent cause of eye discharge in cats is an upper respiratory tract infection, commonly referred to as cat flu. The two principal culprits are feline herpesvirus type 1 (FHV-1) and feline calicivirus (FCV). These viruses are extremely widespread — FHV-1 in particular is thought to be latent in the majority of the cat population, with stress or illness triggering recurrent episodes throughout a cat's life.
During an active infection, cats typically show watery to mildly mucoid discharge from one or both eyes, alongside sneezing, nasal discharge, and lethargy. Secondary bacterial infection can cause the discharge to turn thick and yellow or green. The Advisory Board on Cat Diseases (ABCD), a European expert panel that publishes evidence-based guidelines on feline infectious diseases, recommends core vaccination against FHV-1 and FCV as essential for all cats regardless of lifestyle. Vaccination does not prevent infection entirely but significantly reduces the severity of clinical signs.
2. Conjunctivitis — Bacterial and Allergic
Conjunctivitis, or inflammation of the conjunctiva (the pink tissue lining the inner eyelids and the surface of the eye), is the second most frequently diagnosed cause of feline eye discharge. It can be caused by bacteria, allergens, irritants, or as a direct consequence of viral infection.
Bacterial conjunctivitis often produces a thicker, more coloured discharge and may cause the eyelids to stick together, particularly after a period of sleep. Allergic conjunctivitis tends to cause clear, watery discharge and is often accompanied by rubbing or pawing at the eyes. Environmental triggers such as pollen, dust, or household cleaning products are common culprits in UK households.
3. Chlamydophila felis
Chlamydophila felis is an intracellular bacterial pathogen that primarily targets the conjunctiva. It is a recognised cause of persistent, often one-sided conjunctivitis in cats, and is particularly common in multi-cat households and rehoming centres. Discharge associated with Chlamydophila tends to be initially clear and watery before progressing to a thicker consistency if left untreated.
Importantly, a non-core vaccine is available for Chlamydophila felis, and the ABCD recommends considering it for cats in high-risk environments. Treatment typically involves a prolonged course of doxycycline. The BSAVA (British Small Animal Veterinary Association) guidelines note that all in-contact cats in a household should be treated simultaneously to prevent re-infection.
4. Blocked Tear Ducts — Epiphora
Epiphora refers to the overflow of tears onto the face due to impaired drainage through the nasolacrimal (tear) ducts. In cats, this is especially common in flat-faced (brachycephalic) breeds such as Persians and Exotic Shorthairs, where the anatomy of the skull compresses or distorts the tear drainage pathway.
The discharge associated with epiphora is typically clear and watery, running down the face from the inner corner of the eye. Over time, the constant moisture can cause reddish-brown staining of the fur, as well as skin irritation or secondary infection in the affected area. Treatment depends on the underlying cause and may include flushing the ducts under sedation or, in some cases, surgical correction.
5. Corneal Ulcers
A corneal ulcer is a break in the surface of the cornea — the transparent outer layer of the eye. It can result from trauma, a foreign body, a scratch during a fight, or from chronic FHV-1 infection, which can directly damage corneal tissue. Corneal ulcers are painful and typically cause a cat to squint, blink excessively, or keep the affected eye partially or fully closed.
The associated discharge is usually watery to mildly mucoid. Any cat showing signs of eye pain alongside discharge should be seen by a vet urgently, as untreated corneal ulcers can deteriorate rapidly and may threaten vision.
What the Type of Discharge Tells You
The appearance of eye discharge is a useful initial indicator of what may be going on, though it should never be used to replace a proper veterinary examination.
- Clear or watery discharge: Often associated with early viral infection, allergies, epiphora, or mild irritation. In isolation and without other symptoms, small amounts of clear discharge may be within normal variation for some cats.
- Thick yellow or green discharge: Strongly suggests bacterial involvement, either as a primary infection or secondary to a viral cause. This type of discharge is more likely to require antibiotic treatment and veterinary input.
- Reddish-brown staining around the eye: Usually indicates chronic overflow of tears (epiphora) rather than active infection. Common in flat-faced breeds.
- Discharge with cloudiness of the eye: May indicate a corneal ulcer, uveitis (inflammation inside the eye), or other serious ocular condition. Seek veterinary advice promptly.
Assessing Both Eyes
Whether discharge affects one or both eyes can be a helpful clue. Bilateral (both eyes) discharge is more typical of systemic infections such as cat flu, where the virus affects the whole body. Unilateral (one eye only) discharge is more suggestive of a localised problem — a foreign body, an injury, or Chlamydophila felis in its early stages. That said, conditions that start in one eye can progress to involve both, so this distinction should be considered alongside all other signs rather than in isolation.
When to See a Vet
Some eye discharge can be monitored at home for a short period, particularly if it is mild, clear, and your cat is otherwise well. However, certain signs indicate that veterinary assessment should not be delayed. The PDSA (People's Dispensary for Sick Animals) recommends seeking advice within 24 hours if you notice any of the following:
- Thick yellow or green discharge from one or both eyes
- Squinting, excessive blinking, or a partially closed eye
- Visible redness, swelling, or cloudiness of the eye
- Your cat pawing or rubbing at its eye repeatedly
- Discharge accompanied by sneezing, nasal discharge, or loss of appetite
- Any sudden change in the appearance of the eye itself
- Discharge that has not improved after 48 hours of home monitoring
Eye conditions in cats can deteriorate quickly, and early treatment nearly always leads to better outcomes. If there is any uncertainty, contacting your vet or a service such as PDSA for guidance is always the right approach.
Home Care and What to Avoid
If your cat has mild discharge and you are waiting for a vet appointment, you can gently clean around the eye using a clean, damp piece of cotton wool, wiping from the inner corner outward. Use a fresh piece for each eye to avoid cross-contamination. Never use human eye drops, antibiotic creams intended for other species, or any product not specifically prescribed or recommended by a vet — many human preparations contain ingredients that are toxic to cats or may worsen the condition.
The Role of Vaccination
Given that upper respiratory infections are the leading cause of eye discharge in cats, keeping vaccinations up to date is one of the most effective preventive measures available. Core vaccines covering FHV-1 and FCV are recommended for all cats by the ABCD and are a standard part of UK veterinary practice. For cats in high-risk settings — rescue centres, multi-cat households, or those with outdoor access — discussing the non-core Chlamydophila felis vaccine with your vet is worthwhile.
Regular veterinary check-ups also allow for early detection of conditions such as blocked tear ducts or chronic herpesvirus activity before they cause significant discomfort. Eye health is closely linked to overall wellbeing, and a small discharge noticed early is far easier to treat than one that has been left to develop.