Cats are masters of disguise. In the wild, showing weakness attracted predators, so domestic cats still hide pain and sickness with remarkable skill — often until an illness is well advanced. That is why knowing the first signs of illness in cats matters so much for UK owners: you are your cat’s early-warning system, and catching problems early is the single biggest factor in successful treatment. The changes to watch for are rarely dramatic. They are whispers, not shouts: a missed meal here, a quieter evening there.

This guide walks through the subtle early signs vets wish owners spotted sooner — changes in appetite, thirst, litter tray habits, behaviour, coat and breathing — plus a simple weekly health check you can do at home, and the red flags that mean “vet now, not tomorrow.”

Why early detection matters so much in cats

Many common feline conditions — kidney disease, hyperthyroidism, diabetes, dental disease — develop gradually and respond far better to early treatment. Chronic kidney disease, for instance, affects around one in three cats over ten, and dietary management started early can add years of good-quality life. The tragedy vets describe most often is the cat brought in “suddenly” ill whose owner, looking back, realises the signs had been building for months.

The Cats Protection health guidance encourages owners to learn their individual cat’s normal — normal appetite, normal water intake, normal energy, normal litter tray output. Illness detection is really change detection, and nobody knows your cat’s baseline better than you.

Appetite and thirst: the earliest tells

A cat that suddenly eats ravenously, or one that picks at food it used to love, is telling you something. Increased appetite with weight loss is the classic signature of hyperthyroidism in older cats; a reduced appetite can signal anything from dental pain to nausea to systemic illness. Any appetite change lasting more than 24 hours deserves attention, and 48 hours warrants a vet call.

Thirst changes are equally revealing. Drinking noticeably more — emptying the bowl faster, seeking taps or puddles — can indicate kidney disease, diabetes or hyperthyroidism. Drinking less, especially alongside dry food feeding, risks dehydration and urinary problems. If you have multiple cats, it is worth occasionally monitoring individuals separately so one cat’s increased drinking is not masked by the group.

Litter tray clues

The litter tray is a diagnostic goldmine. Straining, crying, or frequent unproductive trips can signal urinary blockage — a genuine emergency, especially in male cats. Going outside the tray, particularly in a previously reliable cat, often means pain or distress rather than naughtiness. Changes in volume (much larger or smaller clumps), colour, or smell, and any blood, all merit a vet conversation.

Keep trays scrupulously clean — one per cat plus one spare is the behaviourist recommendation — because a dirty tray makes cats avoid it, muddying your observations. Our guide to keeping your house clean when you live with pets includes litter-area setups that make daily monitoring effortless rather than a chore.

Behaviour shifts: the quiet signals

Behavioural change is often the very first sign. A social cat that starts hiding, a lap cat that suddenly avoids touch, or a quiet cat that becomes clingy — all can indicate pain or nausea. Increased vocalisation, especially at night in older cats, can signal hypertension, thyroid issues or cognitive decline. Irritability when handled, reluctance to jump, or sleeping in new, lower spots may point to arthritis, which is hugely underdiagnosed in cats.

Energy matters too. Cats sleep a lot anyway — 12 to 16 hours — but a cat that stops playing, stops greeting you, or seems “flat” is communicating. PDSA’s cat health advice suggests filming concerning behaviours on your phone; a 30-second video of a limp, a breathing pattern or a litter-tray visit is enormously helpful to your vet.

Coat, eyes, nose and breathing

A cat that stops grooming develops a dull, unkempt or matted coat — often the first visible sign of illness, mouth pain, or arthritis that makes twisting painful. Conversely, over-grooming bald patches on the belly or legs can indicate stress, allergy or pain. Eyes should be bright and clear; persistent squinting, discharge or a visible third eyelid warrants investigation. Watch breathing at rest: consistently rapid, laboured or open-mouth breathing is abnormal and, if sudden, an emergency.

Weight is the vital sign owners miss most. Weigh your cat monthly — bathroom scales work if you weigh yourself holding the cat and subtract. Gradual weight loss is easy to miss under fluff but is one of the most significant early indicators vets rely on.

The five-minute weekly health check

Once a week, run through this routine: feel the body for lumps, weight change and rib coverage; check ears for odour or dark discharge; look at eyes and nose; lift the lip to check gums (pink, not pale, yellow or brick red) and teeth; run hands against the fur for mats or bald patches; watch the cat walk for stiffness; note litter tray output. Five minutes, once a week, builds an intimate knowledge of your cat’s normal that no vet — seeing your cat for ten minutes a year — can match.

Red flags: vet now, not tomorrow

Some signs bypass “wait and see” entirely: open-mouth breathing or severe breathing difficulty; straining to urinate with little or no output (especially males); repeated vomiting; collapse, seizure or extreme lethargy; a suspected poisoning; or a cat that has not eaten for 24 hours. Travel can also unmask hidden issues — stress suppresses the immune system — so if you are planning time away, read our guide to pet-friendly holidays in the UK for advice on minimising travel stress and arranging proper care cover.

Conclusion

Your cat will probably never tell you plainly that something is wrong — that is not how cats work. But they do tell you, in missed meals and quieter evenings, in fuller water bowls and fuller litter trays, in a coat gone dull and a jump no longer attempted. Learning to hear those whispers is the most valuable skill a cat owner can develop. Watch the baseline, run your weekly five-minute check, film anything odd, and never feel silly calling the vet about a “small” change. In feline medicine, the small changes are the whole story — and catching them early is what turns a crisis into a footnote.

Frequently Asked Questions

How can I tell if my cat is in pain?

Look for hiding, reduced activity, reluctance to jump, changes in grooming, altered facial expression (squinted eyes, flattened ears), and new irritability. Cats rarely cry out; behavioural change is the main signal.

My cat is drinking more water — is that bad?

It can be an early sign of kidney disease, diabetes or hyperthyroidism, especially in older cats. Mention it to your vet, who may suggest blood and urine tests to investigate.

How often should a healthy cat see the vet?

Annually for adult cats, with vaccinations as advised, and every six months for cats over ten or those with chronic conditions. Senior cats benefit from yearly blood pressure and blood tests.

Is it normal for older cats to slow down?

Some slowing is normal, but significant lethargy, weight loss or behaviour change is not “just old age” — many causes are treatable. Always have new changes checked rather than attributing them to age.