15 Warning Signs Your Cat Is Sick — And What To Do About Each One

Cat Health • Veterinary Advice

Medically reviewed against guidance from the American Association of Feline Practitioners (AAFP) and Cornell University College of Veterinary Medicine. Updated March 2026.

Cats are magnificent deceivers. Millions of years of evolution have hardwired them to suppress visible signs of weakness — because in the wild, a sick animal is a vulnerable target. This survival instinct hasn’t disappeared in your pampered house cat. The result: by the time your cat looks sick, the underlying condition may have already progressed significantly.

A 2023 study published in the Journal of Feline Medicine and Surgery found that more than 30% of cats examined at routine wellness appointments had a previously undetected health condition — despite owners reporting no obvious symptoms. This isn’t owner negligence. It is the direct result of feline instinct, and it is exactly why knowing the early, subtle warning signs can — quite literally — save your cat’s life.

Warning Sign #1: Changes in Appetite

Any significant deviation from your cat’s normal eating habits deserves attention. Loss of appetite (anorexia) is one of the most common indicators of illness — but it’s also one of the most dangerous for cats specifically, due to a condition called hepatic lipidosis (fatty liver disease).

When cats stop eating for even 24–48 hours, the body begins mobilizing fat stores at a rate the liver cannot process efficiently. The result is fat accumulation in liver cells, impairing function. According to the Cornell University College of Veterinary Medicine, hepatic lipidosis is the most common liver disease in cats and can develop with frightening speed — particularly in overweight cats.

Conversely, a sudden increase in appetite paired with weight loss is a classic presentation of hyperthyroidism or diabetes mellitus — both common in middle-aged and senior cats, and both highly manageable when caught early.

Warning Sign #2: Increased Thirst and Urination

Polydipsia (excessive thirst) and polyuria (excessive urination) occurring together are a textbook signal of three major conditions: chronic kidney disease (CKD), diabetes mellitus, and hyperthyroidism.

CKD is shockingly prevalent in cats. Research published in the Journal of Veterinary Internal Medicine found it affects approximately 1 in 3 cats over the age of 12. The condition is insidious — cats can lose up to 75% of kidney function before showing any outward signs. Increased water intake is often the first detectable clue. If your cat has started drinking from unusual sources (taps, toilets, plant saucers) that they previously ignored, take note.

Warning Sign #3: Litter Box Abnormalities

The litter box is arguably your most valuable early-warning diagnostic tool. Daily cleaning is not just hygiene — it’s surveillance. Changes to watch for:

• Straining to urinate with little or no output (especially in males): This is a life-threatening emergency. Urinary obstruction is fatal within 24–48 hours without treatment — do not wait overnight.
• Blood in urine: Indicates feline lower urinary tract disease (FLUTD), bladder stones, infection, or in rare cases, bladder cancer.
• Urinating outside the box: Often a sign of a urinary tract infection, a painful condition associated with the box, or anxiety.
• Diarrhea lasting more than 24 hours: Can cause dangerous dehydration rapidly, especially in kittens.
• No feces for 48+ hours: May indicate constipation, megacolon, dehydration, or intestinal obstruction.

The American Association of Feline Practitioners recommends one litter box per cat plus one additional — and daily cleaning to enable you to monitor output effectively.

Warning Sign #4: Unexplained Weight Changes

Cats can lose significant body mass before it becomes visually apparent — particularly in long-haired breeds where fur obscures the body’s profile. Incorporate a weekly hands-on check: run both hands along your cat’s ribcage. You should feel ribs with gentle pressure but not see them. A sharp, prominent spine or easily visible ribs signals significant weight loss requiring investigation.

Weight loss is associated with more than 20 different medical conditions in cats, including hyperthyroidism (affecting roughly 10% of cats over age 10), inflammatory bowel disease (IBD), intestinal lymphoma, CKD, and dental pain that makes eating uncomfortable. Weight gain accompanied by a distended abdomen can indicate fluid accumulation related to heart disease, liver disease, or feline infectious peritonitis (FIP).

Warning Sign #5: Coat and Grooming Changes

Healthy cats dedicate 30–50% of their waking hours to grooming. Deviations in either direction are medically significant.

Over-grooming (psychogenic alopecia) — excessive licking, particularly in focused patches — suggests allergies, skin parasites (fleas or mites), localized pain, or anxiety. Cats lick to soothe discomfort, and repeated focus on one area often indicates a problem beneath the surface.

Under-grooming — a dull, matted, or unkempt coat in a previously fastidious cat — signals that your cat is either in pain (making twisting to groom difficult), depressed, or systemically unwell. Senior cats who stop grooming their lower back and hindquarters commonly have arthritis making those areas painful to reach.

Warning Sign #6: Lethargy and Hiding

While cats sleep 12–16 hours a day, genuine lethargy looks different from rest. A sick cat typically becomes unresponsive to stimuli that would normally engage them — favorite treats, play invitations, your return home. They may seek unusual hiding places (under beds, inside closets) — an instinctive behavior linked to the sick animal’s drive to be alone and undisturbed.

If your cat is limply unresponsive, shows no interest in food or interaction for more than 12–24 hours, or seems to have lost their personality entirely, these are serious red flags requiring same-day veterinary attention. Lethargy accompanies virtually every major feline illness, from infection and toxin ingestion to heart disease and cancer.

Warning Sign #7: Vomiting — Normal vs. Emergency

Occasional vomiting (once or twice monthly) in an otherwise healthy, active cat is generally within the range of normal. However, the following patterns require prompt veterinary attention:

• Vomiting more than 2–3 times per day
• Vomiting blood (bright red or dark, coffee-ground appearance)
• Vomiting accompanied by lethargy, anorexia, or weight loss
• Repeated, forceful retching without producing material (can indicate foreign body obstruction)
• Chronic intermittent vomiting (weekly or more) — a hallmark of IBD and intestinal lymphoma

Warning Sign #8: Respiratory Changes

Healthy cats breathe quietly and effortlessly at 15–30 breaths per minute at rest. Any labored, rapid, or noisy breathing is a serious emergency. If your cat is breathing with mouth open, this is an emergency — seek care immediately. Cats do not pant normally like dogs; open-mouth breathing in a resting cat indicates severe respiratory distress.

Causes include feline asthma, pleural effusion (fluid around the lungs — common in heart disease), pneumonia, or laryngeal paralysis. Resting respiratory rates consistently above 40 breaths/minute are abnormal. The Royal Canin Cardiology Support app provides a free tool to help owners count and track resting respiratory rates — invaluable for cats with known heart conditions.

Warning Signs #9–15: Additional Red Flags

• #9 — Eye or nasal discharge: Persistent colored (yellow/green) discharge indicates upper respiratory infection, conjunctivitis, or dental disease causing sinus involvement.
• #10 — Third eyelid visible (nictitating membrane): The pale inner eyelid showing at the corner of the eye almost always signals illness, dehydration, nerve damage, or pain. Also called Haw’s syndrome.
• #11 — Vocalization changes: Increased howling or yowling, especially at night in senior cats, often indicates cognitive dysfunction, hyperthyroidism, or high blood pressure.
• #12 — Bad breath (halitosis): Severe oral odor is not normal. It can indicate dental disease (affecting over 70% of cats over age 3), kidney disease (ammonia breath), or diabetes (sweet/fruity breath).
• #13 — Swollen abdomen: Visible belly distension suggests fluid accumulation (ascites), intestinal obstruction, or in unspayed females, pyometra — a potentially fatal uterine infection.
• #14 — Lumps or swellings: Any lump under the skin warrants veterinary examination. Feline injection-site sarcomas, while rare, are aggressive and can appear at vaccine sites.
• #15 — Neurological symptoms: Sudden wobbling, head tilting, circling, or seizures require immediate emergency care — possible causes include vestibular disease, toxin ingestion, brain tumor, or stroke.

Emergency Symptoms: Go Now, Don’t Wait

Your Monthly Home Health Check

Veterinarians recommend a brief monthly hands-on check between annual wellness exams. Here’s a simple 5-minute routine:

• ✅ Weight: Weigh on a baby scale; track monthly. A 10% change warrants a call to your vet.
• ✅ Body condition: Feel ribs, spine, and hip bones. Should be felt but not prominent.
• ✅ Eyes: Clear and bright with no discharge, squinting, or cloudiness.
• ✅ Ears: Clean, no odor, no dark discharge or scratching.
• ✅ Mouth: Pink gums (not white, yellow, or blue), no strong odor, no obvious broken teeth.
• ✅ Coat and skin: No bald patches, excessive dandruff, bumps, or mats.
• ✅ Movement: No limping, hesitation jumping, or stiffness rising from rest.
• ✅ Behavior: Normal appetite, interaction level, litter box use.

Keep a simple monthly log. What matters most is change — subtle trends you’d miss without records become obvious patterns that often lead to early diagnoses.

The Bottom Line

Your cat’s greatest vulnerability is also their greatest strength: they are extraordinarily good at appearing fine. Your job as their owner is to know them well enough to catch the moments when they’re not. The investment of attention — weekly hands-on checks, consistent litter box monitoring, annual (and biannual for seniors) veterinary exams — pays returns measured in years of healthy life together.

When something feels off, even if you can’t articulate exactly what — trust that instinct. Experienced veterinarians consistently report that owner concern is one of the most reliable early indicators that something is medically wrong. The cost of a precautionary exam is always worth it.