Cats get pink eye (conjunctivitis) through viral infections, bacterial infections, or exposure to environmental irritants. The most common cause by far is feline herpesvirus, which spreads through direct contact between cats and can reactivate throughout a cat’s life. Bacterial infections and allergens account for most remaining cases.
Viral Infections Are the Leading Cause
Feline herpesvirus type 1 (FHV-1) is the single most common reason cats develop pink eye. The virus spreads through close, usually direct contact with an infected cat. It is extremely contagious, and most cats who spend time in shelters, rescues, or multi-cat environments will be exposed at some point. Even cats with no visible symptoms can carry and transmit the virus.
What makes herpesvirus especially persistent is what happens after the initial infection clears. The virus retreats into nerve cells and goes dormant, essentially hiding from the immune system. When a cat is stressed, sick, or otherwise run down, the virus escapes from those nerve cells and travels back out along the nerves, causing symptoms to return. This is why a cat can seem perfectly healthy for months or years, then suddenly develop red, watery eyes after a move, a new pet in the household, or a bout of illness.
Kittens are particularly vulnerable. Feral kittens, outdoor kittens, and shelter kittens face compounding risks: immature immune systems plus stressors like poor nutrition, fleas, and cold temperatures. Feline calicivirus, another common respiratory virus, can also cause conjunctivitis, though it more frequently presents as mouth ulcers and sneezing.
Bacterial Infections
The bacterium Chlamydia felis is the most significant bacterial cause of feline pink eye. It can be isolated in up to 30% of cats with conjunctivitis, while fewer than 3% of healthy cats carry it. Transmission happens through close contact, with ocular fluids being the primary source of infection. Sneezing can also spread the organism. This makes multi-cat households, catteries, and shelters high-risk environments.
Mycoplasma felis is another bacterium linked to feline conjunctivitis. It naturally lives on the respiratory membranes of some cats, so not every cat carrying it will get sick. It spreads from cat to cat through aerosol droplets and grooming. One important detail: this bacterium cannot survive long outside a host, so indirect transmission (through shared bowls or bedding, for example) is unlikely. Mycoplasma can act as either a primary cause of eye and respiratory disease or as an opportunistic invader that worsens an existing viral infection.
In many cases, bacterial conjunctivitis develops as a secondary infection on top of a viral one. A cat with herpesvirus-damaged eye tissue is more susceptible to bacteria colonizing those weakened surfaces, which is why a viral case that starts with clear, watery discharge can progress to thick, yellow-green discharge over several days.
Environmental Irritants and Allergies
Not all feline pink eye is infectious. Dust, airborne chemicals (cleaning products, cigarette smoke, aerosol sprays), and certain outdoor plants can irritate the conjunctiva and trigger inflammation. This type is called allergic conjunctivitis. It tends to cause redness and watering without the thick discharge seen in bacterial cases, and it often affects both eyes equally. Removing the irritant usually resolves symptoms without further treatment.
How to Tell What Type Your Cat Has
The character of your cat’s eye discharge offers clues about the cause. Clear, watery discharge is more typical of viral infections or allergens. Mucus-like or greenish-yellow discharge points toward a bacterial infection, either primary or secondary to a virus. Swelling of the tissue around the eye, squinting, and a visible third eyelid are common across all types.
If only one eye is affected, a foreign body, injury, or localized infection is more likely. Both eyes being red and watery at the same time suggests a systemic cause like a respiratory virus or an airborne irritant. Sneezing, nasal discharge, or lethargy alongside the eye symptoms strongly suggests an upper respiratory infection rather than a simple irritant.
Which Cats Are Most at Risk
Kittens, shelter cats, and cats in multi-cat households face the highest risk of infectious conjunctivitis simply because close contact is the primary transmission route for both viruses and bacteria. Cats who go outdoors and interact with unfamiliar animals also have greater exposure. Immunocompromised cats or those already fighting another illness are more likely to develop symptoms from organisms they might otherwise keep in check.
Cats with a history of herpesvirus infection carry lifelong risk of recurrence. Any significant stressor, from boarding to surgery to the introduction of a new pet, can trigger a flare-up.
Prevention
Core feline vaccines (the combination vaccine covering herpesvirus, calicivirus, and panleukopenia) provide good general protection against the two main viral causes of pink eye. These vaccines don’t completely prevent infection, but they significantly reduce the severity and duration of symptoms. Intranasal versions of the vaccine offer faster protection, which is especially useful for kittens and cats about to enter high-risk environments like boarding facilities.
A separate vaccine exists for Chlamydia felis, though it is not considered core and is typically recommended only for cats in multi-cat environments with known exposure risk. Beyond vaccination, reducing stress, keeping living spaces clean, and isolating new or symptomatic cats from the rest of the household are the most practical steps for preventing spread.
Can You Catch Pink Eye From Your Cat?
The risk is very low, but not zero. Chlamydia felis has been documented in rare human cases, transmitted through contact with infected ocular or respiratory secretions. Basic hygiene, particularly washing your hands after handling a cat with eye symptoms, effectively minimizes this already small risk. Feline herpesvirus does not infect humans.