How to Tell If Your Cat Is Sick

Cats are prey animals as well as predators. In the wild, showing weakness invites attack. This evolutionary pressure means domestic cats are instinctively driven to hide signs of illness for as long as possible. By the time a cat is visibly unwell, the underlying condition has often been present for days, weeks or in chronic cases months. Learning to read the early and subtle signs of illness is one of the most valuable skills a cat owner can develop.

At Bangkok Cats, monitoring the health of every cat in the cattery is part of the daily routine. When you are responsible for champion breeding cats, catching changes early is not optional. The observations that follow are what we look for, and they apply equally to any cat in any home in Thailand.

Changes in eating behaviour

A healthy cat has a consistent relationship with food. It knows when meals are coming, it shows interest when food is prepared and it eats with reasonable enthusiasm. Any significant departure from this baseline is worth noting.

A cat that suddenly stops eating entirely is a concerning sign. Unlike dogs, cats cannot safely fast for extended periods. A cat that goes without food for more than twenty-four to forty-eight hours is at risk of hepatic lipidosis, a serious liver condition where the body mobilises fat stores faster than the liver can process them. This is one of the few feline health emergencies where the speed of onset can be measured in days rather than weeks. If your cat refuses more than one or two meals in a row without an obvious environmental explanation such as extreme stress from a visitor or a move, contact your vet.

A sudden increase in appetite is less obviously concerning but can signal conditions including hyperthyroidism, diabetes or intestinal parasites. A cat that has always been a moderate eater and suddenly demands food constantly, loses weight despite eating more, or vocalises excessively around mealtimes warrants investigation.

Changes in how a cat eats can also be informative. A cat that approaches its bowl, sniffs the food and walks away may be experiencing nausea or dental pain that makes eating uncomfortable rather than a simple loss of appetite.

Changes in water intake

Raw-fed cats drink very little water because they obtain most of their hydration from food. A raw-fed cat that suddenly starts drinking from a water bowl more than occasionally is showing a change worth noting. For cats on dry food, water intake is harder to track as a baseline, but a noticeable increase in drinking, or finding the cat at the water bowl repeatedly throughout the day, is a flag for conditions including kidney disease, diabetes and hyperthyroidism. All three are common in middle-aged and older cats.

Litter box changes

The litter box tells you a great deal about a cat's health if you pay attention to it. Healthy cats on a raw diet produce small, firm, low-odour stools. Any significant change from your cat's individual baseline is informative.

Loose stools or diarrhoea that lasts more than forty-eight hours needs attention. A single loose stool from a dietary change or minor stress is usually self-resolving. Persistent diarrhoea indicates infection, parasites, inflammatory bowel disease or other gastrointestinal problems that need diagnosis.

Straining in the litter box, particularly in male cats, is an emergency. A male cat that repeatedly enters the litter box, strains and produces little or no urine is potentially obstructed. Urethral obstruction is fatal within twenty-four to forty-eight hours if untreated. This is one of the signs that should send you to an emergency vet immediately, not the next day.

Blood in the urine, visible as pink, red or brown colouration in the litter or on the litter tray, always warrants same-day veterinary attention even if the cat is not in obvious distress.

A cat that stops using the litter box entirely is almost always communicating either a medical problem such as urinary tract pain or a behavioural or environmental issue. Do not dismiss litter box avoidance as bad behaviour before ruling out a physical cause.

Changes in behaviour and personality

You know your cat's normal personality better than anyone. Trust your observations when something feels off. A cat that is normally sociable and interactive but suddenly becomes withdrawn, hides persistently or stops responding to usual interactions is showing a change in behaviour that almost always has a physical cause in an otherwise stable environment.

Conversely, a normally calm cat that becomes suddenly restless, irritable or aggressive without an obvious environmental trigger may be in pain. Pain in cats is often expressed as irritability, increased vocalisation, reluctance to be handled or aggression when touched in a particular area. If your cat hisses or reacts sharply when you touch a specific body part that it normally tolerates, that location is worth examining and discussing with a vet.

A sudden change in vocalisation pattern is also meaningful. A cat that never vocalises and begins crying or yowling, particularly at night, may be in pain or experiencing the cognitive changes associated with feline dementia in older cats.

Physical signs to check regularly

Getting into the habit of doing a quick physical check on your cat weekly makes it much easier to notice changes early. This does not need to be a formal examination. It can happen naturally during handling and grooming.

Eyes should be bright and clear. Discharge, cloudiness, persistent squinting, visible third eyelid or asymmetry between the two eyes all warrant veterinary assessment.

Nose should be clean. A small amount of clear discharge is normal. Coloured discharge, crusting, or frequent sneezing suggests upper respiratory infection.

Mouth and gums should be pink and moist. Pale, white, grey or yellow gums are serious warning signs. Pale gums can indicate anaemia or shock. Yellow gums indicate jaundice and liver involvement. Gums that are tacky or dry rather than moist suggest dehydration. Bad breath beyond a mild food smell can indicate dental disease or kidney problems.

Coat should be smooth and clean. A cat that stops grooming will develop a dull, matted or greasy coat. Grooming cessation is a reliable sign of illness in a cat that previously maintained itself well. Conversely, over-grooming to the point of bald patches usually indicates stress, anxiety or a skin condition.

Weight and body condition should be stable. Muscle wasting along the spine, hips and shoulders is common in older cats with kidney disease, hyperthyroidism or cancer. Running your hands along the spine weekly means you notice this earlier than it becomes visible.

Breathing should be quiet and effortless at rest. Open-mouth breathing in a cat that is not overheated or just finished vigorous exercise is always a serious sign requiring immediate veterinary attention. Laboured breathing, rapid breathing at rest or breathing with visible effort from the sides and abdomen are all emergencies.

Signs that require same-day or emergency veterinary attention

Some signs should never be met with a wait-and-see approach. The following require contact with a vet on the same day or immediate emergency attendance.

Straining to urinate with little or no output, particularly in male cats. Open-mouth or laboured breathing. Sudden inability to use the hind legs. Collapse or extreme weakness. Seizures. Suspected poisoning or toxin ingestion. Pale, white, grey or yellow gums. Suspected injury from a fall or impact. Severe vomiting or diarrhoea with blood. Inability to eat or drink for more than twenty-four hours.

We covered one of the most common household toxins for Thai cats in detail in our article on why paracetamol can kill cats. Knowing the symptoms of paracetamol poisoning specifically is important given how common it is in Thai households.

Building a baseline for your cat

The most useful thing you can do as a cat owner is to know your individual cat's normal. What does it normally eat and how much? How often does it use the litter box and what does normal output look like? How does it normally behave throughout the day? How much does it normally weigh?

A monthly weight check, a weekly coat and body check, and daily observation of eating and litter box habits give you a reliable baseline. Changes from that baseline are the signal. Without a known baseline, changes are much harder to detect.

For a comprehensive guide to keeping your cat healthy across all life stages, our complete cat health guide covers vaccinations, dental care, weight management, parasite prevention and senior cat care in full detail.

Frequently asked questions

How do I know if my cat is just tired or actually sick?
Context matters. A cat that sleeps more than usual after an active day or during very hot weather is probably just tired. A cat that is consistently lethargic across multiple days, is less interested in food, and does not respond to its normal triggers for activity such as play or feeding time is showing a pattern worth investigating. Single observations are less meaningful than patterns over two or three days.

My cat vomited once. Should I be worried?
Single vomiting episodes in cats are common and often not serious. Cats vomit from hairballs, eating too fast, minor dietary indiscretion and mild stress. A cat that vomits once, appears normal afterwards and continues eating and drinking normally usually does not need urgent attention. Repeated vomiting across a day, vomiting accompanied by lethargy or loss of appetite, vomiting with blood, or vomiting in a cat that is also straining to urinate all require veterinary attention.

My cat is eating but seems thinner. What could cause this?
Weight loss despite normal or increased appetite is one of the key signs of hyperthyroidism, diabetes and intestinal malabsorption conditions including inflammatory bowel disease. All three are common in middle-aged and older cats. A vet check including blood work will identify the cause in most cases. Early diagnosis significantly improves treatment outcomes for all three conditions.

How often should I take a healthy cat to the vet?
Annual wellness checks for cats under seven years old and twice yearly from age seven onwards. Blood work annually from age seven to catch kidney, liver and thyroid changes before symptoms develop. Vaccine boosters on the schedule your vet recommends. More frequent visits whenever you notice changes from the baseline described in this article.

My cat hides when it is unwell. How do I find it and assess it?
If your cat is hiding and you are concerned, approach quietly and calmly rather than forcing it out of its hiding spot. Speak softly. Allow it to come to you if possible. When you can get close enough, check gum colour, breathing pattern and whether it responds to gentle touch. These three observations will tell you whether this is a cat that needs urgent veterinary attention or one that needs quiet time to recover from stress.