A sick cat rarely looks sick. It looks like a cat that has started sleeping somewhere new, eating a little less, or grooming a little differently. Cats conceal illness far more effectively than dogs, so the signals that matter are changes in routine rather than obvious symptoms. By the time a cat looks unwell to a visitor, it has usually been unwell for a while.
The short answer
- Illness in cats shows up as changes in routine: where they sleep, how much they eat, how they use the tray.
- A cat that stops eating for 24 hours needs a vet, and 48 hours is genuinely dangerous, not cautious advice.
- A male cat straining in the tray without producing urine is an emergency measured in hours.
- Open-mouth breathing in a cat is never normal and always urgent.
- Drinking noticeably more is one of the most useful early signals owners can actually observe.
Why cats hide illness
Concealing weakness is inherited behaviour, not stoicism. For a small solitary hunter, visible illness attracts predators and loses territory, so the instinct is to withdraw and act normal. Domestication has not removed it.
The practical consequence is that cats skip the early warning phase that dogs give you. There is no limping, no whining, no obvious decline. There is a cat that is slightly less present in the household, and then, later, a cat that is clearly ill.
12 signs worth acting on
1. Hiding, or sleeping somewhere new
The single most reported first sign. A cat that has moved under the bed, behind the sofa or into a wardrobe, and stays there, is usually telling you something. New hiding is more significant than extra sleeping.
2. Eating less, or stopping
Cats are not built to fast. A cat that skips one meal is worth watching; one that has not eaten for 24 hours needs a phone call. See the section below on why this one is different from the same sign in a dog.
3. Weight loss you can feel before you can see
A 5% change is clinically meaningful in a cat, which for a 4.5 kg animal is 225 g. That is invisible across a room and obvious on a scale. Our cat weight chart by breed covers normal ranges and how to weigh at home.
4. Litter tray changes
Volume, frequency, consistency and location all carry information. Larger or more frequent urine clumps point towards kidney disease, diabetes or hyperthyroidism. Sudden toileting outside the tray is more often medical than behavioural, particularly in a cat that was previously reliable.
5. Straining in the tray without producing urine
This deserves its own line. In male cats it can mean a urinary blockage, which becomes life-threatening within a day. A cat going in and out of the tray, crouching, crying, or producing only drops needs to be seen immediately, not tomorrow.
6. Drinking noticeably more
One of the few early signals that is genuinely easy to observe: a cat that starts visiting the water bowl, the tap or the shower tray far more than usual. Increased thirst and urination together are a classic presentation of chronic kidney disease, diabetes and hyperthyroidism, all of which are common in middle-aged and older cats and all of which are better managed when caught early.
7. Grooming that changes in either direction
A scruffy, greasy or matted coat in a cat that used to be immaculate usually means it has stopped grooming, which is a common sign of pain, nausea or arthritis. The opposite, over-grooming one area until it is bald, points to pain, itch or stress in that spot.
8. Vomiting that is not a hairball
Regular vomiting is not normal in cats, despite the folklore. Occasional hairballs are one thing; vomiting more than about once a month, or any vomiting with lethargy or weight loss, warrants investigation. Intestinal parasites are a common and easily treated cause, covered in how often to deworm a cat.
9. Breathing changes
Count breaths while the cat sleeps: a resting rate consistently above about 30 breaths per minute is worth reporting. Open-mouth breathing, panting, or an effortful belly-heaving pattern is an emergency.
10. Reduced jumping and new stiffness
Cats rarely limp. They just stop doing things: no longer jumping onto the windowsill, taking the sofa in two steps instead of one, sleeping downstairs. Arthritis is common in older cats and consistently under-diagnosed because it looks like slowing down. The 2022 AAHA pain management guidelines treat this quiet loss of function as a core sign.
11. A change in voice or night-time yowling
New loud vocalising at night in an older cat is worth a check rather than an assumption about age; hyperthyroidism, high blood pressure and cognitive change all present this way. A hoarse or altered voice is its own signal.
12. Visible third eyelid
The pale membrane appearing across the inner corner of the eye when the cat is awake is a non-specific but real sign that something systemic is wrong.
Read nextDiabetes in Cats and Dogs: Symptoms, Early Signs and When to WorryWhat needs a vet today
| Sign | Why it cannot wait |
|---|---|
| Straining to urinate, especially a male cat | Possible blockage; life-threatening within a day |
| Open-mouth breathing or laboured breathing | Respiratory or cardiac emergency |
| Not eating for 48 hours | Risk of liver failure, see below |
| Collapse, seizure or unresponsiveness | Immediate assessment needed |
| Pale, white or blue gums | Anaemia, shock or oxygen shortage |
| Repeated vomiting with lethargy | Obstruction, toxin or metabolic crisis |
| Known or suspected toxin ingestion | Treatable early, much harder later; see foods toxic to dogs and cats |
Why a cat that will not eat is different
This is the part that surprises most owners. When a cat stops eating, its body mobilises fat into the liver faster than the liver can process it, which can cause hepatic lipidosis, or fatty liver. Overweight cats are at highest risk, and the condition can develop after just a few days without food.
That is why the advice for cats is stricter than for dogs. A dog that skips a day is usually fine. A cat that skips a day needs a phone call, and a cat that has eaten nothing for 48 hours needs to be seen. Tempting with warm, strong-smelling food is reasonable for a few hours; it is not a plan for the weekend.
Sick cat or ageing cat?
Ageing does not cause symptoms. It raises the likelihood of conditions that do. Sleeping more is typical in an older cat; sleeping in a new hiding place is not. Being less playful is typical; stopping jumping entirely is not. Drinking a bit more on hot days is typical; a permanent change in thirst is not.
The useful test is whether something has changed, not whether the cat is old. The FelineVMA practice guidelines recommend more frequent check-ups for senior cats precisely because these conditions are common, treatable and quiet.
What to bring to the appointment
A cat consultation is short and the cat will not be helping. What makes the difference is a timeline: when the change started, how often it happens, whether it is worse at a particular time, what else changed in the household, and current weight with a previous weight to compare against.
A photo or short video of the behaviour is worth more than a description, particularly for breathing, gait and straining, since none of those reproduce on demand in a consulting room.
Make the change visible
Almost every sign on this list is a comparison rather than an observation. Something is different from before, and before is exactly what memory handles badly.
PetVitals records weight with dates, logs symptoms with severity, and charts the trend, so a 300 g decline over four months appears as a slope instead of a feeling. It also keeps vaccination and parasite dates in one place. The same principle applies to dogs, where the signals differ but the method does not, covered in signs your dog is in pain.
This article is general educational information, not veterinary advice, and it cannot diagnose your cat. If you notice any of these changes, contact your veterinarian.