Cats are famously independent and masters at hiding discomfort. This can make it tricky to tell when something’s wrong. As an ER veterinarian and cat mom, I’ve seen how quickly subtle changes can turn into something more serious. The earlier you spot the signs, the better your chance of helping your cat feel better. In this article, I’ll walk you through the most common physical and behavioral symptoms of illness in cats. I’ll also share when to keep an eye on things, and when it’s time to call your vet.
In this article:
How to tell if your cat is sick
Cats don’t usually come right out and show signs of illness when it starts. More often, the signs are subtle at first, then get more obvious as the illness progresses. Paying attention to your cat’s daily habits is the best way to catch early signs of trouble.
Physical symptoms
Respiratory issues
Sneezing, coughing, nasal discharge, noisy breathing, or open-mouth breathing can be signs of an upper respiratory infection, asthma, or even heart disease. If your cat is breathing faster than normal or seems to be working harder to breathe, it’s time to get them checked out by a veterinarian as soon as possible.
Weight loss
Unintentional weight loss is a red flag. Even if your cat seems to be eating normally, gradual weight loss over time can signal conditions like hyperthyroidism, kidney disease, or cancer.
Vomiting
Occasional hairballs are usually not a cause for concern, but frequent vomiting is not normal. If your cat is vomiting multiple times a week or suddenly begins vomiting more often, it could be due to gastrointestinal issues, a foreign body obstruction, or a more serious systemic illness.
Diarrhea or constipation
Changes in stool consistency, frequency, or litter box habits can point to digestive problems, dietary intolerance, stress, or underlying illness. Constipation, especially in older cats, can also be a warning sign.
Changes in coat or skin
A dull coat, greasy fur, bald patches, or excessive scratching could indicate skin infections, parasites, or internal disease. Cats are typically avid groomers, so poor coat condition often points to an underlying problem.
Bad breath or drooling
Dental disease is very common in cats and can cause pain, infection, and eating difficulties. Bad breath, excessive drooling, or pawing at the mouth are reasons to visit your vet.
Limping or mobility changes
An injury may be present if your cat is suddenly less active, reluctant to jump, or limping. These signs could be arthritis, traumatic injury, or even neurological problems.
Twitching or tremoring
If you notice an eye twitching or facial muscles tremoring or shaking, go see your veterinarian. Seizures in cats are not always full body convulsions. In fact, they often show up in much subtler ways at first.
Behavioral changes
Cats are creatures of habit, and any shift in their usual routine can be a clue that something isn’t right.
Changes in eating or drinking habits
A decrease or increase in appetite, sudden food pickiness, or drinking more or less than usual can point to issues like dental pain, kidney disease, or diabetes. Track how much your cat is eating and drinking over time.
Litter box changes
Urinating more frequently, peeing outside the box, straining, or producing smaller amounts of urine can all signal urinary issues, which can become emergencies if left untreated. Diarrhea, constipation, or very dry stools also warrant attention.
Personality shifts
A normally social cat who starts hiding or a calm cat who suddenly acts aggressively might be in pain or sick. Sudden clinginess or restlessness can also be signs something is off.
Changes in energy level
Lethargy is a common early sign of illness. If your cat is sleeping more than usual, no longer playing, or seems weak, it’s a good idea to check in with your veterinarian.
Other subtle signs your cat may be sick
Sometimes, the early signs of illness are so mild they’re easy to miss. Here are a few more things to keep an eye on:
- A new or persistent meow that seems unusual
- Hiding in new places or avoiding family members
- Change in grooming habits (overgrooming or not grooming at all)
- Sitting in a hunched position
- Sudden disinterest in favorite activities or toys
- Increased vocalization, especially at night
Cats often communicate through changes in behavior. If something seems off, trust your gut and go see your veterinarian.
When to “wait and see”
Mild symptoms that last less than 24 hours and resolve on their own, like a single vomit episode or a skipped meal, can sometimes be monitored at home. Make sure your cat is otherwise acting normal: alert, eating or drinking within the next 12 hours, and using the litter box.
Keep a journal of what you observe and note any patterns or worsening symptoms. If things don’t improve or you notice new signs, call your vet. With a self-cleaning litter box like Litter-Robot and the Whisker app, you can stay informed with real-time insights into litter box activity, weight trends, and more—even in multi-cat homes.
When to call your vet
Call your veterinarian if:
- Your cat has been vomiting or having diarrhea for more than 24 hours
- You notice weight loss, even if your cat seems fine otherwise
- There’s a change in urination, especially straining or going outside the box
- Your cat stops eating or drinking for more than 24 hours
- Behavior changes persist longer than a day or two
- You see signs of pain, such as limping or vocalizing when touched
Your vet may recommend an exam, blood work, or imaging depending on your cat’s history and symptoms.
When to take your cat to the emergency vet
Some situations call for immediate action. Bring your cat to an emergency vet if you notice:
- Labored or open-mouth breathing
- Inability to urinate (especially in male cats)
- You notice facial twitching or seizure-like activity
- Sudden collapse or fainting
- Severe bleeding
- Continuous vomiting or diarrhea
- Sudden and persistent vocalization
- Pale gums or sudden weakness
If you’re unsure whether it’s an emergency, it’s always better to call and ask.
Final thoughts
Cats are resilient and often hide pain until it becomes too much. That’s why it’s so important to know what’s normal for your cat and act on any changes you notice. A small shift in behavior or appetite might be your only clue that something more serious is brewing. Don’t wait too long to ask for help. Early action can make a big difference in outcomes and peace of mind.
