Feline Upper Respiratory Tract Infections — What Every Cat Owner Needs to Know

A Sick Cat Is a Quiet Alarm

Your cat does not sneeze the way you do. A human sneeze is an explosion; a cat’s is often a tight, nasal sputter that you hear three or four times before you realize what it was. That is usually the first signal that something is working its way through the delicate lining of the upper airway, and by the time the second or third sign shows up—clear eye goop, a dull coat, a bowl of untouched food—the infection has already been incubating for days. Feline upper respiratory tract infections (URIs) are the most common infectious disease seen in cats of every age. This guide walks you through what is happening inside that small nose, what your veterinarian is looking for, and what you can do at home.

The Usual Suspects: What Is Actually Making Your Cat Sick

When people say a cat has a “cat cold,” they are usually describing one of a handful of pathogens, and the most important thing to understand is that the overwhelming majority are viral. Studies of feline respiratory disease consistently find that about 90% of cases are caused by just two organisms: feline herpesvirus type 1 (FHV-1) and feline calicivirus (FCV). FHV-1 is the feline version of the human cold-sore virus. It never truly leaves the body; after the initial infection resolves, the virus hides in nerve tissue and can reactivate during stress, releasing virus again and producing fresh clinical signs. That is why a cat can have “another cold” that looks identical to the first years later—it often is.

Feline calicivirus works differently. It does not establish the same lifelong latency, but it mutates readily and is famous for causing painful ulcers in the mouth and on the tongue. There is even a severe systemic variant of FCV that causes widespread tissue damage, though it remains rare. Two other bacteria complete the picture. Chlamydophila felis primarily attacks the conjunctiva—the pink tissue lining the eyelids—and is a major cause of the swollen, weeping eyes you see in catteries. Mycoplasma species and Bordetella bronchiseptica (the same bacterium behind some kennel cough in dogs) round out the list, and they more often show up as secondary invaders on top of a viral infection than as sole causes.

Here is the part most owners find surprising: co-infections are the rule, not the exception. A cat can carry FHV-1 and FCV at the same time, and a bacterial pathogen can climb aboard once the virus has damaged the airway lining. Treating one and not the others is a common reason a “cold” drags on.

Read The Signs: From a Runny Nose to a Sealed Shut

The classic URI unfolds in a fairly predictable order. Sneezing usually comes first, followed within a day or two by nasal discharge. Early on that discharge is thin and clear—it is mostly mucus and serum. As the infection progresses, and especially if bacteria move in, the discharge thickens and turns yellow or green, which tells your vet that a secondary bacterial component has developed. The same progression happens in the eyes. Conjunctivitis makes the lids red and swollen, and in severe cases the discharge can crust over and glue a cat’s eyes shut. FHV-1 in particular can ulcerate the cornea, the clear front surface of the eye, and those ulcers are painful enough that a cat will squint, paw at its face, or avoid bright light.

What you cannot see but your cat feels is the loss of smell. Cats rely far more on scent than we do, and a congested nose suppresses appetite not because food is unattractive but because it is unrecognizable. A cat that suddenly stops eating during a URI may simply be smelling nothing at all. Add fever, lethargy, and the deep tiredness of an active immune response, and you have a cat that wants only to sleep in a warm spot. Feline calicivirus adds its own signature: ulcers on the tongue, gums, and roof of the mouth, often with drooling because swallowing has become painful. If your cat is drooling or smacking its lips, calicivirus should be high on the list.

How Your Veterinarian Actually Figures This Out

There is no single blood test that says “this cat has a URI,” and most of the time a good clinical exam is enough to start treatment. Your vet will take a thorough history—vaccination status, whether the cat has been around other cats, how long the signs have been present, what the discharge looks like now versus at the start. That history alone frequently separates a viral picture from a bacterial one. A cat with sudden onset of sneezing, clear discharge, and no fever is classically viral. A cat that has been sick for a week with thick green discharge and a fever has almost certainly developed a secondary bacterial infection, and that distinction steers the treatment.

When the picture is unclear or the cat is not responding, veterinarians reach for more specific tools. PCR testing can detect the genetic material of FHV-1 and FCV directly from swabs of the mouth, nose, or conjunctiva, and it is sensitive enough to identify which virus is present. Bacterial culture from a swab can identify Chlamydophila, Mycoplasma, or Bordetella and tell your vet which antibiotic will actually work. What your vet is doing, in other words, is ruling things out—checking that this is not a foreign body stuck in the nose, a dental abscess draining into the sinuses, a fungal infection, or, in a very young kitten, a congenital problem like a cleft palate. URIs are common, but not every sniffle is a URI.

Treatment: Supporting the Body So It Can Do the Work

Here is the honest truth that changes how you think about treatment: there is no drug that kills FHV-1 or FCV the way an antibiotic kills a bacterium. For the vast majority of URIs, the treatment is supportive care—keeping the cat hydrated, fed, comfortable, and strong enough for its own immune system to clear the infection. This is not a concession; it is the standard of care. Dehydration is the single most common complication because a cat that cannot smell food stops eating and a cat with a sore throat stops drinking. Fluids—under the skin at the clinic or by syringe at home—are often the single most important intervention.

Nutrition is a close second. Warming food releases its aroma, which a congested nose can partially pick up even when a cat cannot smell normally. Offering strong-smelling, palatable food, or adding a little warmed broth, can be enough to trigger a few bites. In more stubborn cases, appetite stimulants are available and safe under veterinary guidance. Humidification helps too: running a humidifier or taking the cat into a steamy bathroom for ten minutes loosens dried mucus and makes breathing easier.

Eyes need attention because ophthalmic disease is where URI complications turn serious. Artificial tear lubricants keep the surface of the eye moist when discharge is crusting it over, and if a corneal ulcer is present, a vet-supervised plan—possibly including an antiviral ointment—is essential to protect vision. Antiviral drugs do exist. Famciclovir is the most commonly used systemic antiviral for FHV-1; it is a human antiviral repurposed for cats, and while clinical evidence is still accumulating, many veterinary ophthalmologists reach for it in herpes-driven disease that is not resolving, particularly when the eyes are involved.

Where do antibiotics fit? Only when there is evidence of a secondary bacterial infection—thick purulent discharge, fever, a positive culture—or when treating an organism like Chlamydophila felis that is bacterial from the start. Giving an antibiotic for a purely viral URI does nothing for the virus and only risks resistance. Your veterinarian makes that call based on the examination, and the choice of drug is targeted to the organism involved. If you want the details of antimicrobial therapy, that topic is covered in a companion article.

One supplement deserves a fair hearing because you will see it everywhere: lysine. For years, L-lysine was promoted to suppress FHV-1 replication, and for a long time it was a staple of feline URI management. The evidence has not held up. Several controlled trials found no measurable benefit of lysine for cats infected with FHV-1, and at high doses it can actually raise arginine requirements. Most current veterinary guidance views lysine as largely ineffective. If you are considering it, a better conversation with your vet is about cat lysine supplementation done safely and with realistic expectations. For a deeper dive into the virus itself, the feline herpesvirus guide for pet parents walks through transmission, latency, and long-term management in detail.

Home Care That Makes a Measurable Difference

Most URIs are managed at home under veterinary direction, and there are concrete things you can do beyond waiting it out. Run a cool-mist humidifier in the room where the cat rests, or bring the cat into the bathroom while you shower, and keep the nose clean by gently wiping away discharge with a warm, damp cloth—cats cannot effectively clear their own noses the way we blow ours, so dried discharge genuinely blocks airflow. If the cat is eating very little, syringe-feeding a smooth, high-calorie recovery food every few hours can prevent hepatic lipidosis, a dangerous liver condition that develops when a cat stops eating for too long.

Stress is a hidden driver of URI severity, and this is especially true with FHV-1, which reactivates under stress. Keep the environment calm: a quiet room away from loud noises and other pets, familiar bedding, food and water within easy reach, and a predictable routine. If you have multiple cats, isolate the sick one until it recovers. URI pathogens spread through droplets from sneezing and through contaminated bowls, bedding, and your own hands, so wash your hands between cats and do not share bowls or toys. Recovery is rarely instant—some cats feel better in a few days, but a full recovery often takes a week or two.

Vaccination and Prevention: Reducing the Blow

The single most effective preventive tool is the FVRCP vaccine, which is a core vaccine recommended for every cat regardless of lifestyle. The “R” stands for rhinotracheitis (FHV-1) and the “C” for calicivirus, so it targets exactly the two viruses behind 90% of URIs. The critical caveat, and one that surprises many owners: the FVRCP vaccine does not prevent infection. A vaccinated cat can still become infected and can still shed virus. What it reliably does is reduce the severity of disease and shorten the course, which is why vaccinated cats in shelters and multi-cat homes have far less severe URIs.

Vaccination is not the whole story. Stress management is prevention, because stress is what wakes a dormant herpesvirus from hiding. For a new cat entering the household, that means a slow, quiet introduction, not an immediate face-to-face with the resident cats. In multi-cat homes, hygiene is a constant: wash food and water bowls regularly, change litter frequently, and keep new arrivals isolated for a quarantine period before they join the group.

When It Stops Being a Cold and Starts Being an Emergency

Most URIs are miserable but self-limiting. Some are not, and the line matters because delayed care is what turns a treatable URI into a crisis. Bring your cat to the veterinarian promptly if it stops eating for more than 24 to 48 hours—anorexia in a cat is never a waiting game. Severe ocular disease is another red line: if the eyes are swollen shut, if the discharge is excessive, or if you see cloudiness or a visible change in the eye itself, do not wait. Respiratory distress—open-mouth, labored, or belly breathing—is an emergency that can indicate the infection has descended into the lungs, where a URI can become pneumonia. Young kittens, geriatric cats, and any immunocompromised cat (including those with feline leukemia or feline immunodeficiency virus) are at higher risk for severe disease and should be seen earlier. When in doubt, call your vet.

Frequently Asked Questions

References

• Feline upper respiratory tract disease: a review of the literature — PubMed
• Feline herpesvirus-1: clinical and virologic aspects — PubMed
• Famciclovir for the treatment of feline herpesvirus-1 infection — PubMed

Disclaimer

This article is for educational purposes only and is not a substitute for professional veterinary advice, diagnosis, or treatment. Every cat is different, and what is appropriate for one may be harmful to another. Always consult a licensed veterinarian before starting, changing, or stopping any treatment, and seek immediate veterinary care for any emergency signs such as difficulty breathing, prolonged anorexia, or severe ocular disease.