Cat eye infections are most often caused by feline herpesvirus, which accounts for the majority of infectious conjunctivitis cases. Bacteria, physical injuries, eyelid abnormalities, and environmental irritants round out the list. Understanding which type your cat is dealing with helps explain what you’re seeing and what to expect during recovery.
Feline Herpesvirus: The Most Common Cause
Feline herpesvirus type 1 (FHV-1) is the single biggest driver of eye infections in cats. The virus directly damages cells in the surface layer of the cornea, causing ulcers with a distinctive branching pattern. Once the immune system responds to the virus, that inflammatory reaction can itself damage deeper layers of the cornea, leading to cloudiness and scarring over time.
About 80% of cats that catch FHV-1 become lifelong carriers. Of those carriers, roughly 45% will spontaneously reactivate the virus at some point, either shedding it without symptoms or developing a visible flare-up. Stress is the classic trigger for reactivation: a move, a new pet in the house, surgery, pregnancy, or illness can all bring the virus back. Immunosuppressive medications, including corticosteroid eye drops, can do the same.
A typical FHV-1 flare starts with watery discharge from one eye, then spreads to both eyes within one to three weeks. The discharge often thickens from clear and watery to yellowish-green as the infection progresses. You may also notice your cat squinting, holding one eye partially shut, or pawing at their face.
Bacterial Infections
Two bacteria cause most primary bacterial eye infections in cats. Chlamydia felis produces a chronic, low-grade conjunctivitis. It typically starts in one eye and spreads to the other, with discharge that progresses from watery to thick and mucus-like. Cats with chlamydial infections may sneeze occasionally but generally don’t seem as sick as cats with herpesvirus.
Mycoplasma species tend to cause more dramatic swelling of the conjunctiva (the pink tissue lining the eyelids) along with milder nasal symptoms. The swelling can make the tissue look puffy and almost balloon-like around the eye.
Bacteria also show up as secondary invaders. When a viral infection or a scratch damages the eye’s surface, bacteria can colonize the wound and make things worse. This is why a simple corneal ulcer sometimes turns into a deeper, more serious infection if left untreated.
Scratches, Foreign Bodies, and Trauma
Physical injury is a common non-infectious cause of eye problems that can quickly become infectious. Cat fights pose a particularly high infection risk because claws introduce bacteria directly into the cornea. A blade of grass, a wood chip, or a bit of litter trapped under the third eyelid can scrape the corneal surface repeatedly, creating an entry point for bacteria or fungi.
Chemical exposure matters too. Cleaning products, aerosol sprays, or anything that contacts the eye’s surface can cause a chemical burn and subsequent ulceration. Once the cornea is damaged, the outer layer may heal over the wound while trapping bacteria or fungi underneath, forming a deeper pocket of infection called a stromal abscess. This is one reason even minor-looking eye injuries deserve attention.
Eyelid and Lash Abnormalities
Some cats are born with structural problems that set them up for chronic eye irritation. Entropion, where the eyelid rolls inward so that fur and lashes rub against the cornea, is the most common culprit. That constant friction damages the surface of the eye day after day, creating opportunities for infection.
Persians and Maine Coons are significantly more likely to develop entropion than other breeds. In a French study of breed-related eye diseases, Maine Coons had roughly 13 times the odds of entropion compared to the general cat population, and Persians about 3.4 times the odds. Maine Coons were especially prone to entropion on the outer corner of the lower eyelid, while Persians more often had it on the inner corner. Other structural issues like ectopic cilia (lashes growing from abnormal spots), eyelid agenesis (missing sections of eyelid), and dermoids (small skin-like growths on the eye surface) can cause similar chronic irritation.
Environmental and Household Irritants
Not every red, watery eye is an infection. Dust, pollen, mold spores, cigarette or vape smoke, essential oil diffusers, strong cleaning products, and perfumes can all irritate a cat’s eyes and cause non-infectious conjunctivitis. The symptoms look similar to early infection: redness, watery discharge, squinting. The difference is that irritant-related inflammation tends to improve when the source is removed, while infections persist or worsen. However, ongoing irritation can weaken the eye’s defenses enough to let an actual infection take hold, so the line between the two isn’t always clean.
Immune-Suppressing Diseases
Cats with feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV) face higher risks of eye problems for different reasons. FIV weakens the immune system over time, and about 11% of FIV-positive cats in one study had chronic conjunctivitis. FIV also causes chronic inflammation inside the eye (uveitis), which can require long-term treatment. Because their immune defenses are compromised, FIV-positive cats are also more vulnerable to secondary infections from herpesvirus, Chlamydia, or bacteria that a healthy cat’s immune system would keep in check.
FeLV primarily threatens the eyes through lymphosarcoma, a type of cancer that can develop in the tissues of the eye, including the iris, conjunctiva, or the space behind the eye. Feline infectious peritonitis, caused by a mutated coronavirus, can also trigger uveitis. Any cat showing signs of inflammation deep within the eye, such as a cloudy appearance, color changes to the iris, or persistently dilated pupils, should be tested for these underlying viruses.
What Eye Discharge Tells You
The appearance of your cat’s eye discharge offers clues about what’s happening, though it’s not a perfect diagnostic tool. Clear, watery discharge usually points to the early stages of a viral infection, an irritant, or allergies. As the condition progresses or bacteria get involved, the discharge thickens and turns whitish, yellow, or green. Brown crusting around the eyelids often accompanies infections that have been going on for days or longer. Thick, mucus-like discharge with significant conjunctival swelling leans toward Mycoplasma or Chlamydia. A discharge that starts in one eye and moves to the other over a couple of weeks is a hallmark of both herpesvirus and chlamydial infection.
Recovery Timelines
Most bacterial and viral eye infections resolve within 5 to 14 days with appropriate treatment. Bacterial infections typically respond to topical antibiotic eye drops or ointments. Viral infections are often self-limiting, meaning the cat’s immune system clears the active flare on its own, though antiviral eye medications can shorten the course and reduce corneal damage.
The catch with herpesvirus is that recovery from one episode doesn’t prevent future ones. Cats remain carriers for life, and flare-ups can recur during stressful periods. Chlamydial conjunctivitis can also linger or come back if antibiotic treatment is stopped too early. Structural problems like entropion will continue causing irritation and secondary infections until they’re corrected surgically.
Reducing the Risk
The FVRCP vaccine, which covers feline herpesvirus, calicivirus, and panleukopenia, is the most important preventive tool. It doesn’t prevent infection entirely, but it significantly reduces the severity of disease. The intranasal version can begin providing protection against herpesvirus challenge as early as four days after a single dose, making it useful even in outbreak situations like shelters. Keeping cats indoors reduces exposure to fights, foreign bodies, and contact with infected strays. Minimizing environmental stress, maintaining good air quality in your home, and keeping up with routine veterinary exams all help lower the odds of both new infections and herpesvirus reactivation.