Feline herpesvirus (FHV-1) is the most common respiratory pathogen in cats, and its telltale signs are sneezing, nasal discharge, and watery or goopy eyes. Most cats pick it up as kittens, and once infected, they carry the virus for life. It can stay dormant for months or years and then flare up during stressful periods. Here’s how to recognize it and what to expect.
The Main Signs to Watch For
The classic presentation of feline herpes looks a lot like a bad cold. Your cat may sneeze frequently, sometimes in fits of several sneezes in a row. You’ll likely notice discharge from the nose that starts clear and watery but can turn thick and yellowish-green if a secondary bacterial infection sets in. The same progression often happens with eye discharge: it begins as excessive tearing and can become crusty or mucus-like.
Beyond the sneezing and discharge, affected cats commonly show:
- Squinting or holding one eye shut, a sign of pain or irritation in the eye
- Red, swollen conjunctiva (the pink tissue lining the eyelids), giving the eyes an inflamed appearance
- Lethargy and reduced appetite, partly because congestion dulls their sense of smell and cats rely heavily on scent to find food appealing
- Fever, which you may not notice directly but can contribute to low energy and hiding behavior
In more severe or recurring cases, the virus can cause corneal ulcers, which are small erosions on the surface of the eye. These sometimes develop a branching, tree-like pattern that veterinarians call dendritic ulcers, and they’re considered a strong indicator of herpes specifically. If your cat is pawing at one eye, keeping it closed, or the eye looks cloudy, that warrants prompt attention since untreated ulcers can damage vision.
How It Differs From Other Cat Infections
Feline herpes isn’t the only virus that causes upper respiratory symptoms in cats. Feline calicivirus is responsible for roughly half of all respiratory infections in cats, and sometimes both viruses strike at the same time. Knowing the differences can help you describe what you’re seeing to your vet.
Calicivirus tends to cause ulcers on the tongue, gums, and roof of the mouth. If your cat is drooling, reluctant to eat, or you can see sores inside their mouth, calicivirus is more likely the culprit. Calicivirus can also cause mild limping or joint stiffness, which herpes does not. Herpes, on the other hand, is far more likely to involve the eyes. Significant eye inflammation, corneal ulcers, and heavy eye discharge point more toward herpesvirus than calicivirus. In practice, though, the overlap is significant enough that a vet visit is the most reliable way to distinguish the two.
How Vets Confirm the Diagnosis
Many veterinarians diagnose feline herpes based on the combination of symptoms alone, especially when eye involvement is prominent. But when confirmation matters, the most reliable test is a PCR swab. Your vet takes a small sample from your cat’s eye, nose, or throat using a cotton swab, and the lab checks it for viral DNA. Results typically come back within a few days.
One important caveat: a negative PCR result doesn’t always rule herpes out. During dormant periods, the virus hides in nerve cells and may not show up on a swab. If your cat has recurring flare-ups with the right symptom pattern, your vet may still treat it as herpes even without a positive test. Blood tests that look for antibodies aren’t very useful for diagnosis because so many cats have been exposed to the virus at some point in their lives, and vaccination also produces antibodies.
What Triggers Flare-Ups
Once a cat is infected with feline herpes, the virus never fully leaves the body. It retreats into nerve tissue and reactivates when the immune system is under pressure. Stress is the single biggest trigger. Moving to a new home, introducing a new pet, boarding, a change in routine, or even a trip to the vet can bring on symptoms within days.
Other common triggers include illness from an unrelated cause, surgery or anesthesia, and medications that suppress the immune system. Some cats flare frequently, every few months, while others go years between episodes. The pattern tends to be individual to each cat, so once you’ve lived with a herpes-positive cat for a while, you’ll start to recognize its personal triggers.
How Feline Herpes Spreads
The virus spreads primarily through direct contact with nasal and eye discharge, and through contaminated objects like food bowls, bedding, and your hands. Droplets from sneezing can carry it short distances. Contrary to what many people assume, true airborne transmission across a room is not a major route. This means good hygiene and physical separation are effective ways to protect other cats in your household during a flare-up.
The virus is fragile outside a cat’s body. Standard household disinfectants kill it readily, so routine cleaning of shared items is enough to prevent environmental buildup. Feline herpes cannot infect humans or dogs.
Treatment and Home Care
There’s no cure for feline herpes, but flare-ups are manageable. Your vet may prescribe an antiviral medication given by mouth, typically for one to three weeks depending on the severity. Eye drops or ointments, sometimes antiviral and sometimes antibiotic to prevent secondary infection, are common for cats with eye involvement. If the infection leads to thick, colored nasal discharge or worsening lethargy, antibiotics may be added to address bacterial complications.
At home, you can do several things to keep your cat comfortable during a flare-up. Congested cats benefit from humidity: bring your cat into the bathroom while you run a hot shower for 10 to 15 minutes, a few times a day, to help loosen nasal mucus. Gently wipe away discharge from the nose and eyes with a damp tissue to prevent crusting and skin irritation. Since congestion kills their sense of smell, switch to a strong-smelling canned food or warm their food slightly to make it more appealing. Dehydration is a real risk when cats stop eating, so monitor their water intake closely.
Reducing stress in the household is one of the most effective long-term strategies. Predictable routines, quiet spaces, vertical territory like cat trees, and pheromone diffusers can all help keep flare-ups less frequent and less severe.
A Note on L-Lysine
L-lysine supplements are widely sold for cats with herpes, and many well-meaning sources still recommend them. However, multiple studies have failed to show that lysine reduces the severity or frequency of feline herpes flare-ups. Some research has even suggested it could worsen outcomes by lowering blood levels of another amino acid that the immune system needs. Most veterinary infectious disease specialists no longer recommend it. If you’ve been giving your cat lysine without seeing improvement, this is likely why.