Cat herpes, formally called feline herpesvirus 1 (FHV-1), most visibly shows up as red, watery eyes with discharge, a runny nose, and frequent sneezing. In less common cases, it causes crusty, ulcerated skin lesions on the face. Around 80% of cats that catch the virus carry it for life, with visible symptoms flaring up during periods of stress.
Eye Symptoms Are the Hallmark
The eyes are where cat herpes is most obvious. Early on, you’ll notice redness in the tissue lining the eyelids (the conjunctiva) along with a clear, watery discharge. Over several days, that discharge thickens and turns yellowish or greenish as mucus and pus mix in. Both eyes are usually affected, though one may look worse than the other. The tissue around the eyes can also swell, giving the cat a puffy, squinting appearance.
By about four days into an active infection, the surface layer of the conjunctiva starts breaking down. This is why severely affected cats sometimes have eyes that look “glued shut” with crusted discharge, especially after sleeping.
Deeper in the eye, the virus can cause corneal ulcers. The earliest form is a branching, tree-like pattern on the surface of the cornea that’s essentially unique to herpes in cats. These tiny ulcers are impossible to see with the naked eye and require a vet to apply a fluorescent dye and use a special light. If untreated, these small branching ulcers can merge into larger, irregular “geographical” ulcers that pose a serious threat to the cat’s vision. Many progress so quickly that the early branching stage is never even caught.
Nasal and Respiratory Signs
Alongside the eye symptoms, most cats with an active flare-up develop a runny nose and bouts of sneezing. The nasal discharge follows the same pattern as the eyes: it starts clear and watery, then becomes thicker and discolored with mucus and pus as the infection progresses. Cats with heavy nasal congestion may breathe through their mouths, lose interest in food (since they can’t smell it), and sound congested or raspy.
Skin Lesions on the Face
This is less common but distinctive. Some cats develop ulcerative skin disease, primarily on the face. The affected areas show redness, raw erosions, and open ulcers, often covered with thick crusts. The most typical locations are the nose, the bridge of the muzzle, and the skin around the eyes. Ulcers can also appear inside the mouth.
In rare cases, these skin lesions spread beyond the face to the chest, flanks, abdomen, back, or limbs. When a vet examines a biopsy of these lesions under a microscope, they find extensive ulceration and crusting with characteristic viral signatures inside the skin cells.
How to Tell It Apart From Calicivirus
Feline calicivirus causes similar sneezing and discharge, so the two are easy to confuse. The key visual difference is the mouth. Calicivirus is the virus that typically causes tongue ulcers and sores inside the mouth. Herpes tends to hit the eyes and nose much harder, with corneal ulcers and facial skin lesions being its signatures. If your cat has prominent mouth sores but relatively clear eyes, calicivirus is more likely. If the eyes are the main problem, herpes is the usual suspect.
How Long a Flare-Up Lasts
After a cat is first exposed to the virus, symptoms typically appear within two to five days. An active episode, whether it’s the first infection or a later recurrence, generally lasts 10 to 20 days. During that window and for up to three weeks after symptoms start, the cat is contagious to other cats. The virus does not spread to humans or dogs.
Because the virus goes dormant in nerve tissue, most cats experience repeated flare-ups throughout their lives. About 29% of latently infected cats shed the virus spontaneously even when they look healthy.
What Triggers Visible Symptoms
Stress is the primary trigger for reactivation. Symptoms typically reappear 4 to 11 days after a stressful event. Common triggers include:
- Environmental changes: moving to a new home, boarding, or switching from group housing to a kennel
- Household disruptions: new pets, unfamiliar people, changes to feeding schedules
- Sensory stressors: loud noises, strong odors, uncomfortable temperatures
- Lack of enrichment: boring or confined environments without hiding spots or stimulation
Surgery, illness, or anything else that suppresses the immune system can also bring on a flare.
How Flare-Ups Are Managed
The primary antiviral used for cat herpes is famciclovir, an oral medication given until about a week after symptoms resolve. Treatment focuses on controlling the severity and duration of flare-ups rather than eliminating the virus, which stays dormant for life.
For eye-specific symptoms, vets may prescribe antiviral eye drops or ointments, particularly if corneal ulcers are present. Keeping the cat’s face clean, maintaining humidity to ease congestion, and warming food to make it more aromatic can help with comfort and appetite during a flare.
One widely sold supplement, L-lysine, has been marketed for years as a herpes treatment for cats. A comprehensive review of the evidence found it is not effective for preventing infection, reducing symptoms, or shortening flare-ups. The researchers recommended an immediate stop to lysine supplementation, noting that two clinical trials actually suggested it may enhance viral replication. Despite this, many pet stores and even some veterinary clinics still sell it.
It’s also worth knowing that two common human herpes antivirals, acyclovir and valacyclovir, are toxic to cats. They can cause serious damage to the kidneys, liver, and bone marrow. Never give a cat a human herpes medication without veterinary guidance.