Common Cat Illnesses and Warning Signs to Watch For

Cats evolved to hide illness. A weak cat in the wild is a target, so the instinct to mask discomfort is deeply ingrained even in housecats. This makes early detection genuinely hard, and it is why veterinary care often arrives later for cats than for dogs. The good news is that most common feline illnesses produce subtle behavioral signs days or weeks before they become obvious. Learning to spot them is one of the most valuable skills a cat owner can develop. This guide covers the most frequent conditions and the warning signs that should prompt a vet call.

Important disclaimer

This article is general information for cat owners, not personalized veterinary advice. Always consult your own veterinarian for diagnosis and treatment of any specific concern. When in doubt, call your vet; most clinics have a triage nurse who can advise whether a symptom needs immediate attention.

The universal warning signs

Across most cat illnesses, certain changes are early signals worth noticing:

• Appetite changes. Eating noticeably more or less than usual.
• Thirst changes. Drinking visibly more (refilling the bowl more often) or less.
• Urination changes. More frequent trips, larger volumes, smaller volumes, straining, or accidents outside the box.
• Weight changes. Gradual loss or gain over weeks.
• Energy and behavior. Hiding more, sleeping more, less interactive, or unusually clingy.
• Grooming changes. Less grooming (greasy or matted coat) or overgrooming (bald patches, scabs).
• Litter box changes. Diarrhea, constipation, blood, or going outside the box.
• Breathing changes. Faster breaths at rest, open-mouth breathing, audible breathing.

Any persistent change from your cat’s normal baseline lasting more than 48 to 72 hours deserves a vet visit. Acute or severe symptoms warrant a same-day appointment.

Chronic Kidney Disease (CKD)

The single most common chronic illness in middle-aged and senior cats. Approximately 30 to 40 percent of cats over 10 years old show some degree of kidney dysfunction.

Early signs:

• Increased water consumption.
• Increased urine output (larger clumps in the litter box).
• Gradual weight loss despite normal appetite.
• Mildly dull coat.

Later signs:

• Decreased appetite.
• Vomiting.
• Bad breath (uremic smell).
• Mouth ulcers.
• Pronounced weight loss and dehydration.

What to do: Annual bloodwork from age 7 onward catches kidney changes early. Modern treatment (specialized diet, fluid therapy, phosphorus binders) can extend quality life for years.

Hyperthyroidism

Overactive thyroid is extremely common in older cats. Often appears in cats 10+ years old.

Early signs:

• Increased appetite paired with weight loss.
• Hyperactivity or restlessness.
• Increased thirst.
• Vocalizing more, especially at night.
• Vomiting.

What to do: A simple blood test (T4 level) confirms diagnosis. Treatment options include daily medication, prescription diet, radioactive iodine therapy (often curative), and surgery.

Diabetes

Increasingly common in indoor cats, especially overweight cats and certain breeds (Burmese, Maine Coon).

Early signs:

• Increased thirst and urination.
• Increased appetite.
• Weight loss despite eating well.
• Sticky urine (the wet patches in litter feel tacky).

Later signs:

• Lethargy.
• Weakness in the back legs (diabetic neuropathy).
• Sudden weight loss.

What to do: Bloodwork and urinalysis confirm diagnosis. Many diabetic cats achieve remission with weight loss, dietary changes, and insulin therapy. Early intervention dramatically improves outcomes.

Urinary Tract Issues (FLUTD)

Feline Lower Urinary Tract Disease is a category that includes infections, crystals, stones, idiopathic cystitis, and life-threatening blockages.

Warning signs:

• Straining to urinate.
• Frequent trips to the box with small volume produced.
• Blood-tinged urine.
• Urinating outside the box.
• Vocalizing during urination.
• Excessive grooming of the genital area.

Emergency sign: A male cat (or occasionally a female) straining without producing urine is a urinary blockage and requires immediate emergency care. Untreated, it is fatal within 24 to 48 hours.

What to do: Any urinary symptom warrants a same-week vet visit. Suspected blockage is an immediate emergency.

Dental Disease

Affects roughly 70 percent of cats over 3 years old. Often overlooked because symptoms are subtle.

Signs:

• Bad breath (more than mild fishy breath).
• Visible tartar on teeth.
• Red or bleeding gums.
• Dropping food while eating.
• Preferring soft food.
• Pawing at the mouth.
• Tooth grinding.

What to do: Annual dental check starting at age 3. Professional dental cleaning under anesthesia every 1 to 3 years depending on individual buildup. Daily or every-other-day toothbrushing with cat-safe enzymatic paste slows progression.

Upper Respiratory Infections

Common in kittens, shelter cats, and recently adopted cats. Multiple viruses involved (herpesvirus, calicivirus) plus bacterial secondary infections.

Signs:

• Sneezing.
• Eye discharge (clear or colored).
• Nasal discharge.
• Loss of appetite (due to inability to smell food).
• Lethargy.
• Mild fever.

What to do: Most mild cases resolve in 7 to 10 days with supportive care. Cats with severe symptoms, refusal to eat, or worsening over 3 to 5 days need vet attention.

Inflammatory Bowel Disease (IBD)

Chronic intestinal inflammation, common in middle-aged and senior cats.

Signs:

• Chronic intermittent vomiting.
• Chronic intermittent diarrhea or soft stools.
• Gradual weight loss.
• Decreased appetite.

What to do: Diagnosis usually requires bloodwork, imaging, and sometimes an intestinal biopsy. Treatment includes prescription diet, probiotics, B12 supplementation, and in some cases immunosuppressive medication.

Hypertrophic Cardiomyopathy (HCM)

The most common heart disease in cats. Often silent until advanced.

Signs:

• Often none in early stages.
• Faster breathing at rest (over 30 breaths per minute).
• Open-mouth breathing or panting.
• Sudden weakness or collapse.
• In severe cases, sudden hindlimb paralysis (aortic thromboembolism).

What to do: Annual physical exams include heart auscultation. Breeds at higher risk (Maine Coon, Ragdoll, Persian) benefit from periodic echocardiograms. Sudden breathing changes or limb paralysis are emergencies.

Parasites

Even indoor cats can develop parasite infections from new pets, contaminated soil tracked indoors, or fleas brought home on clothing.

Signs:

• Visible worms in stool or around the anus.
• Scooting the rear on the floor.
• Excessive scratching (fleas).
• Hair loss around the tail base (flea allergy dermatitis).
• Weight loss despite eating well.

What to do: Routine fecal exams at annual vet visits. Monthly preventives recommended in many regions even for indoor cats.

Cancer

Cats develop several forms of cancer, with lymphoma being most common. Risk increases with age.

Signs:

• Lumps that change in size or shape.
• Persistent weight loss.
• Persistent vomiting or diarrhea.
• Sudden change in appetite.
• Difficulty breathing.
• Visible enlargement of the abdomen.
• Wounds that do not heal.

What to do: Annual physical exams catch many tumors early. Any persistent or progressive symptom in a senior cat deserves a thorough workup.

Toxin Exposure

Common household toxins include:

• Lilies (all parts, all species in the Lilium and Hemerocallis genera). Even tiny exposure can cause fatal kidney failure.
• Human medications (acetaminophen, ibuprofen, antidepressants).
• Essential oils (tea tree, peppermint, citrus).
• Antifreeze (sweet taste, highly toxic).
• Rodenticides.
• Insecticides containing permethrin (dog flea products can kill cats).

Warning signs:

• Sudden drooling, vomiting, or staggering.
• Seizures.
• Difficulty breathing.
• Sudden lethargy.

What to do: Any suspected toxin exposure is an emergency. Call your vet or the ASPCA Animal Poison Control hotline immediately. Do not induce vomiting at home without professional guidance.

When to call the vet urgently

Same-day or emergency vet care is needed for:

• Straining to urinate without producing urine.
• Labored breathing, open-mouth breathing, or breathing over 40 breaths per minute at rest.
• Suspected toxin ingestion.
• Seizures.
• Sudden hindlimb paralysis.
• Severe lethargy with refusal to eat or drink.
• Eye injury or sudden change in eye appearance.
• Repeated vomiting (more than 3 times in 12 hours).
• Bloody stool or vomit with significant volume.
• Severe trauma (fall from height, hit by car, attacked by another animal).

Call within 24 to 72 hours for:

• Decreased appetite lasting more than 24 hours.
• Increased thirst or urination noticed over several days.
• Vomiting more than once but less severely.
• Diarrhea lasting more than 24 hours.
• Persistent sneezing or coughing.
• New lameness.
• Behavioral changes lasting several days.

Building a baseline

The most useful tool for catching illness early is knowing what is normal for your cat. Monthly home checks:

• Run hands over the cat to feel for new lumps, bumps, or sore spots.
• Look in the mouth for tartar, red gums, or broken teeth.
• Check the eyes for redness or discharge.
• Note water bowl refill frequency.
• Note litter box clump count and size.
• Weigh the cat monthly (a 10 percent change in either direction is significant).

A baseline notebook (or just notes in your phone) makes subtle changes obvious. The earlier you catch a problem, the better the outcome.

This guide is for general awareness, not diagnosis. Always work with your own veterinarian for medical decisions about your specific cat.

Frequently asked questions

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