How to Tell If Your Cat Has a Fever, and What to Do

A cat's normal body temperature is about 37.5 to 39.2°C (99.5 to 102.5°F). A fever is generally defined as above 39.5°C (103°F), and anything above 40°C (104°F) or a fever lasting more than 24 to 48 hours needs a vet. You cannot judge it by a warm nose or ears — those mean nothing. The only reliable check at home is a digital thermometer in the rectum.

Taking the temperature without a fight

Use a digital thermometer, ideally one kept just for the cat, with a little water-based lubricant. Have a second person hold the cat still, or wrap it in a towel with only the rear end out. Insert about 2 cm into the rectum, angled slightly upward, and wait for the beep. Clean it afterwards with alcohol.

Ear thermometers are convenient but inaccurate in cats, and axillary readings are unreliable. If you cannot take a rectal temperature safely, do not force it — describe the signs to the clinic instead. Never leave a glass thermometer with a cat unattended.

What fever looks like when you cannot measure it

A febrile cat is quiet, hides, stops grooming, and often stops eating. It may sit hunched with its head down, breathe faster, feel warm to the touch along the belly and inner thighs, and shiver or seek cool surfaces. Some cats vomit or have diarrhoea. None of these are specific, which is why the thermometer matters.

A cat that feels cold, has pale gums, or is limp is not febrile in a harmless way — that is shock or collapse and needs emergency care.

Common causes, and why "fever of unknown origin" happens

Infection is the usual explanation: an abscess from a bite wound, an upper respiratory virus, a urinary infection, pneumonia, or a dental infection. In kittens, panleukopenia is a serious possibility. Feline leukemia and feline immunodeficiency virus can cause recurrent fever, and feline infectious peritonitis is another cause vets investigate in young cats with persistent fever.

Non-infectious causes are real too: immune-mediated disease, inflammation, cancer, and reactions to drugs or vaccines. When the basic tests are normal, vets call it fever of unknown origin and work through it in steps rather than guessing.

What you can do at home

Offer water in several places and wet food to keep fluid intake up. Keep the room quiet and comfortably cool, and let the cat rest without being handled. Recheck the temperature every few hours and write down the numbers with the time — a trend tells the vet far more than one reading.

Note appetite, urine and stool output, breathing rate at rest, and any discharge from eyes or nose. Take a short video of anything odd, such as shivering or a strange gait. If other cats are in the house, keep the febrile cat separate and wash your hands between them.

What not to do

Never give paracetamol (acetaminophen) or ibuprofen. A single tablet can kill a cat: paracetamol destroys red blood cells and the liver, and ibuprofen causes acute kidney injury. Aspirin is also unsafe without a vet's dose, and naproxen and diclofenac are worse.

Do not use ice packs, cold baths, or alcohol rubs. Rapid cooling causes shivering, which raises core temperature again, and alcohol is absorbed through the skin. Do not give human antibiotics, and do not assume a fever means antibiotics are needed — most fevers in cats are viral.

Red flags: emergency care now

• Temperature above 40°C (104°F), or above 41°C (105.8°F) at any point.
• Fever with laboured breathing, panting, or a blue-tinged tongue.
• Collapse, seizures, disorientation, or a cat that cannot stand.
• Not eating for more than 24 hours, or no urine for 12 hours.
• Yellow gums, skin, or eyes; small red spots on the gums or belly.
• Repeated vomiting, bloody diarrhoea, or a swollen painful abdomen.
• Any fever in a kitten under 12 weeks, or in a cat that is already unwell.

What the vet will do

Expect a full examination, temperature, hydration check, and bloodwork including a white cell count. Depending on findings, the vet may add a urinalysis, FeLV/FIV testing, imaging, or a fluid sample from the chest or abdomen. Treatment targets the cause; fever itself is a symptom, and it is not always lowered on purpose, because some of the immune response is useful.

Never give a fever-reducing drug at home. If a vet decides one is appropriate, it will be a cat-specific drug at a cat-specific dose, usually a single supervised dose.

After the fever breaks

Appetite usually returns within a day, but full energy can take several days. Weigh the cat a week later, and finish any prescribed course even if it looks well. If the fever returns within a few weeks, say so at the next visit — recurring fever points to a different list of causes than a one-off.

This is general information, not a diagnosis.

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