How to Tell If Your Cat Is Sick: 10 Critical Warning Signs

You know your cat better than anyone. You know how they greet you at the door, how they curl up on the couch, how they sound when they want dinner versus when they want attention. That knowledge is your most powerful tool — because the earliest sign that something is wrong with your cat is almost always a change from their normal.

How to tell if your cat is sick is one of the most important things you can learn as a cat owner. Cats are instinctive hiders of illness — a survival behaviour rooted in the wild, where showing weakness attracts predators. By the time a cat appears obviously unwell, they have often been hiding their symptoms for days, sometimes weeks. Knowing what to look for — before things become obvious — is the difference between early intervention and a health crisis.

This guide covers the 10 most critical warning signs that your cat is sick, what each one means, when to call your vet, and exactly what to do next.

Why Cats Hide Illness — And Why It Makes Them So Difficult to Read

Before diving into the signs, it helps to understand why cats are so good at hiding illness in the first place.

In the wild, a sick or injured animal is a vulnerable animal. Predators target weakness. So cats — even domestic cats thousands of generations removed from the wild — retain the instinct to mask pain, discomfort, and illness until they simply cannot anymore.

This is why your cat may seem “fine” right up until they are not fine at all. It is not stubbornness or stoicism — it is biology. And it is why proactive observation matters more for cats than almost any other pet. As we covered in our guide to how often cats should see the vet — annual wellness exams exist precisely because cats will not tell you when something is wrong.

10 Warning Signs Your Cat Is Sick

Sign 1 — Changes in Appetite: Eating Too Little or Too Much

A sudden change in how much your cat eats is one of the earliest and most reliable signals that something is off.

A cat that has not eaten for more than 24 hours needs attention. Cats are uniquely vulnerable to a dangerous condition called hepatic lipidosis — fatty liver disease — which can develop in as little as 48-72 hours of not eating, particularly in overweight cats. As we explained in detail in our guide to why cats stop eating — do not wait this one out.

Equally important — and more often overlooked — is a sudden increase in appetite. A cat that is ravenously hungry despite eating normally, or that is eating constantly but losing weight, may be showing early signs of hyperthyroidism or diabetes. Both are very manageable conditions when caught early, and both are easy to miss when owners assume a hungry cat is simply a happy cat.

Sign 2 — Changes in Water Intake

Pay attention to the water bowl. A cat that is suddenly drinking significantly more water than usual — or visiting the bowl far more frequently — is displaying one of the most important early warning signs in feline health.

Excessive thirst in cats (polydipsia) is a hallmark symptom of kidney disease, diabetes mellitus, and hyperthyroidism — three of the most common serious conditions in cats, and all three are highly manageable when caught at an early stage. As we covered in our guide to cats drinking a lot of water — a senior cat drinking more water especially should never be dismissed as simply “getting older.”

The opposite — a cat drinking very little or avoiding the water bowl entirely alongside other symptoms — can indicate nausea, pain, or systemic illness.

Sign 3 — Litter Box Changes

The litter box is one of the most valuable health monitoring tools you have — if you are paying attention to it.

Warning signs to watch for include:

Urination changes:

Straining to urinate or producing little to no urine — this is a potential emergency, particularly in male cats. A urinary blockage can become life-threatening within hours.
Blood in the urine — pink or red-tinged clumps in the litter box
Urinating outside the litter box — especially in a cat that has always been reliably trained
Dramatically increased urination alongside increased thirst

Defecation changes:

Diarrhea lasting more than 24-48 hours
Constipation — straining without producing stool, or very infrequent, hard stools
Blood or mucus in the stool
Strong, unusually foul odour to stools

Any sudden change in litter box habits is your cat’s body telling you something. Do not ignore it.

Sign 4 — Lethargy and Unusual Inactivity

Cats sleep a lot — 12 to 16 hours per day is completely normal, as we covered in our guide to why cats sleep so much. So extra sleeping alone is not automatically a warning sign. True lethargy looks different from normal cat sleepiness.

True lethargy is characterised by:

Not responding to stimulation they normally react to — toys, treats, your voice
Unusual location choices — hiding in closets, under beds, in corners
Glassy, dull, or half-closed eyes while awake
Reluctance to move even for food
A general blankness or disconnection from their environment

The key question to ask yourself is: does my cat seem like themselves right now? If the honest answer is no — even if you cannot pinpoint exactly why — that instinct is worth acting on. You know your cat. Trust what you are seeing.

Sign 5 — Vomiting

Cats vomit more readily than most animals, and occasional vomiting — a hairball once every week or two, a single episode after eating too fast — is within the range of normal for many cats.

What is not normal:

Vomiting more than once or twice per week consistently
Vomiting yellow or green bile — which appears when a cat vomits on an empty stomach
Vomiting blood or material that looks like coffee grounds
Vomiting alongside complete food refusal and lethargy
Projectile vomiting
Vomiting that has appeared suddenly and continues for more than 24 hours

Chronic vomiting can indicate inflammatory bowel disease, pancreatitis, kidney disease, hyperthyroidism, food intolerance, intestinal parasites, or an obstruction. Repeated acute vomiting can indicate poisoning, obstruction, or infection. Neither should be watched and waited through for more than 24 hours without a vet call.

Sign 6 — Changes in Breathing

Breathing changes are one of the most urgent warning signs in cats. Unlike some symptoms that can be monitored for a day or two, breathing abnormalities require prompt — sometimes immediate — veterinary attention.

Contact your vet the same day or go to an emergency clinic if you notice:

Breathing that is faster than normal at rest
Laboured breathing — visible effort in the chest or belly with each breath
Open-mouth breathing — cats almost never breathe through their mouths unless severely distressed or overheated
Wheezing, rattling, or crackling sounds during breathing
Blue or pale gums — a sign of oxygen deprivation and a true emergency

Breathing changes in cats can indicate asthma, heart disease, pleural effusion (fluid around the lungs), respiratory infection, or severe anemia. None of these are wait-and-see situations.

Sign 7 — Coat and Skin Changes

A healthy cat has a coat that reflects their inner health — smooth, clean, with a natural shine. Cats are meticulous self-groomers, and when their coat deteriorates, it is almost always because something inside has changed.

Signs to watch for:

Dull, dry, rough, or matted fur — particularly in a cat that has always groomed well
Sudden excessive grooming — over-grooming until patches of fur are thinned or missing
Complete cessation of grooming — a cat that stops cleaning themselves is a cat that is uncomfortable, painful, or depressed
Flaking skin or dandruff
New lumps, bumps, or skin lesions anywhere on the body
Yellowing of the skin or the whites of the eyes — jaundice, which indicates liver disease

Senior cats often groom less thoroughly as mobility decreases — but a sudden change in grooming behaviour at any age is worth investigating. As we covered in our guide to how long indoor cats live — coat quality is one of the most reliable external indicators of overall health.

Sign 8 — Eye and Nose Changes

The eyes and nose offer a clear window into your cat’s health — and changes in either should not be dismissed as minor.

Eye warning signs:

Discharge — watery, cloudy, or thick and coloured
Third eyelid visible (the pink membrane in the inner corner) — this showing prominently is a classic sign your cat is unwell
Squinting or holding one or both eyes partially closed
Cloudiness or change in eye colour
Unequal pupil sizes — one dilated and one constricted

Nose warning signs:

Discharge — clear, white, yellow, or green
Crusting around the nostrils
Repeated sneezing
Nosebleeds

Upper respiratory infections are very common in cats and cause many of these symptoms simultaneously — runny eyes, runny nose, sneezing, and reduced appetite together. While often treatable, they still warrant a vet visit, particularly in kittens and senior cats who are more vulnerable to complications.

Sign 9 — Changes in Behaviour or Personality

This is one of the most important signs — and the most subjective, which is precisely why knowing your individual cat matters so much.

A normally sociable cat that suddenly hides. A usually independent cat that becomes clingy and anxious. A gentle cat that becomes irritable or suddenly aggressive when touched. A playful cat that loses all interest in toys and interaction.

Behavioural changes are how cats express what they cannot show physically — particularly pain. A cat in pain will often:

Withdraw from interaction and hide
Become aggressive or reactive when touched, particularly if you touch the painful area
Stop jumping onto surfaces they normally frequent
Sit hunched with their back rounded rather than their normal relaxed posture
Vocalise more — unusual crying, growling, or yowling

Any significant shift in personality or behaviour that persists for more than a day or two — especially alongside any other symptom — is a reason to call your vet. According to the American Association of Feline Practitioners, behavioural changes are among the most commonly overlooked early indicators of feline illness.

Sign 10 — Weight Changes

Unexplained weight loss or weight gain is one of the most significant health red flags in cats — and also one of the easiest to miss, because it happens gradually.

A cat losing weight slowly over weeks may not look dramatically different day to day. You may not notice until you pick them up and realise they feel lighter than they used to. This is why weighing your cat regularly — monthly for adult cats, bi-monthly for seniors — is genuinely useful.

Weight loss alongside:

Increased appetite → hyperthyroidism or diabetes
Normal or decreased appetite → kidney disease, cancer, inflammatory bowel disease
Vomiting and diarrhea → gastrointestinal disease or parasites

Weight gain alongside:

Increased thirst and urination → possible Cushing’s disease or hypothyroidism (rare in cats)
Lethargy and reduced activity → obesity, which is a condition in itself with serious health consequences

Any unexplained weight change of more than 10% of your cat’s body weight — that is 0.5 kg in a 5 kg cat — is worth discussing with your vet.

How to Tell If Your Kitten Is Sick — Special Considerations

Kittens are more vulnerable than adult cats and deteriorate faster when unwell. The same warning signs apply — but the urgency timeline is shorter.

A kitten not eating for more than 12 hours, showing lethargy, having repeated diarrhea, or displaying any breathing abnormality should be seen by a vet the same day. Kittens have very limited reserves and can decline rapidly.

Additionally, watch for:

Failure to gain weight in the first weeks of life
Pot-bellied appearance alongside a dull coat — often indicates intestinal parasites
Persistent sneezing and eye discharge — upper respiratory infection, very common in young kittens
Pale gums — a sign of anemia or severe illness

If you are unsure whether your kitten is sick or just adjusting to a new home, err on the side of caution and call your vet. A phone consultation costs nothing and gives you professional guidance quickly.

How to Tell If a Stray Cat Is Sick

If you have found a stray cat and are trying to assess their health, look for these visible signs:

Matted, dirty, or patchy fur
Visible wounds, sores, or swelling
Discharge from eyes or nose
Visible ribs or spine — significant underweight
Laboured breathing
Inability to walk normally
Extreme lethargy or inability to stand

A stray cat showing multiple signs of illness should be taken to a vet or animal shelter as soon as possible. Many vets will see stray cats for an initial welfare assessment at a reduced cost — it is always worth calling ahead to explain the situation.

Warning Signs That Need Emergency Veterinary Care — Do Not Wait

Some symptoms require immediate action — not a call to schedule an appointment, but a trip to the nearest emergency vet the same hour.

Go to an emergency vet immediately if your cat shows:

Difficulty breathing or open-mouth breathing
Complete inability to urinate — especially in male cats
Collapse or inability to stand
Seizures
Pale, blue, or white gums
Suspected poisoning or toxin ingestion
Uncontrolled bleeding
Trauma — being hit by a vehicle, a fall from height, or an animal attack
Sudden paralysis or dragging of hind legs — a sign of aortic thromboembolism, a cardiac emergency

Keep the number of your nearest 24-hour emergency veterinary clinic saved in your phone. In a genuine emergency, seconds matter.

What to Do When You Think Your Cat Is Sick — Step by Step

Step 1 — Observe carefully. Note every symptom you can see. When did it start? Is it getting better or worse? Are there multiple symptoms together? The more specific you can be, the more useful the information is to your vet.

Step 2 — Check the basics. Is your cat eating and drinking? Using the litter box normally? Do their gums look pink and moist (normal) or pale and dry (concerning)? Are they responding to you?

Step 3 — Do not wait more than 24 hours. For most symptoms in adult cats, 24 hours is the outer limit of the watch-and-wait approach. For kittens, senior cats, and cats with known health conditions — that window is shorter.

Step 4 — Call your vet. Even if you are not sure whether a visit is warranted, call and describe what you are seeing. Most veterinary practices will advise you over the phone on whether to come in immediately, book an appointment, or monitor for longer.

Step 5 — Do not give human medications. Many over-the-counter pain relievers and medications that are safe for humans are toxic to cats — including ibuprofen, acetaminophen (Tylenol), and aspirin. Never medicate your cat without veterinary guidance.

A Quick-Reference Guide: Symptoms and Urgency

Symptom	Urgency Level
Not eating for 24+ hours	Vet within 24 hours
Vomiting more than twice in 24 hours	Vet within 24 hours
Increased thirst and urination	Vet this week
Litter box changes — straining or blood	Vet within 24 hours
Lethargy and hiding	Vet within 24 hours if alongside other signs
Coat changes or weight loss	Vet this week
Eye or nose discharge	Vet within 24-48 hours
Breathing changes	Same-day or emergency vet
Inability to urinate (male cat)	Emergency vet immediately
Pale or blue gums	Emergency vet immediately
Seizures or collapse	Emergency vet immediately
Behavioural change alone	Monitor 24-48 hours, then vet

FAQ — How to Tell If Your Cat Is Sick

Q: How to tell if my cat is sick or just tired? A: Normal tiredness in cats looks like peaceful, relaxed sleep from which they wake and respond normally. True illness looks like unresponsiveness, hiding, dull eyes, and a general disconnection from their environment even when awake. If your cat is not responding to things that normally interest them — food, their name, a toy — that is not tiredness.

Q: How can I tell if my cat is sick or depressed? A: The symptoms overlap significantly — reduced appetite, lethargy, hiding, reduced grooming, less interaction. The most important thing to know is that depression in cats is almost always caused by something — a loss, a change, an illness. Rule out medical causes first with a vet visit. If the vet clears them physically, address the environmental cause.

Q: How to tell if my cat is sick or just getting old? A: Ageing and illness are not the same thing, though they are often confused. Gradual slowing, sleeping more, and less enthusiasm for play can be normal aspects of ageing. Sudden changes in weight, thirst, appetite, or behaviour are not normal ageing — they are symptoms worth investigating regardless of your cat’s age.

Q: How to tell if a cat is sick or dying? A: A cat that is actively dying will typically stop eating and drinking entirely, withdraw completely, have very laboured or irregular breathing, and become unresponsive. Their gums may be pale or grey. Their body temperature drops. If you believe your cat may be dying, contact your vet immediately — both to provide appropriate comfort care and to assess whether anything can still be done.

Q: How to tell if my cat is not feeling well without visible symptoms? A: Trust your instinct. Changes in how your cat interacts with you, where they choose to spend time, how they hold their body, and whether they seem like themselves are all valid signals — even when no single symptom is obvious. A vet visit prompted by “something just feels off” frequently catches conditions that would otherwise have been missed.

Conclusion

How to tell if your cat is sick comes down to one thing above all else: knowing your cat’s normal and recognising when something has changed. The 10 warning signs in this guide — changes in appetite, thirst, litter box habits, energy levels, vomiting, breathing, coat, eyes, behaviour, and weight — are your roadmap.

None of these signs exist in isolation. A single symptom may be minor. Two or three together are almost always significant. And any symptom that persists beyond 24 hours without improvement deserves professional attention.

Your cat cannot tell you they are not feeling well. But they are showing you — through every change in their behaviour, their body, and their routine. Your job is to notice. And now you know exactly what to look for.

How to Tell If Your Cat Is Sick — 10 Warning Signs Every Owner Must Know