The Cornell Feline Health Center gives the number: in an adult cat, loss of appetite becomes a serious health concern within as little as 24 hours. For a kitten under six weeks, going without food for 12 hours can be a lethal threat. A cat is not a dog that will eat when it is hungry.
When a cat stops eating, fat moves out of storage and into the liver faster than the liver can handle. Cornell calls the result hepatic lipidosis, fatty liver, and says it is almost always preceded by the cat avoiding its food. It is much more common in overweight cats, and in more than 90 percent of cases another illness set it off. The signs are a cat avoiding the bowl, a yellow tinge to the ears and gums, drooling, and hiding away. Cornell says it is likely to be fatal if not treated promptly. Treatment is feeding through a tube, which owners usually continue at home for about a month, and cats that come through it rarely get it again.
Cornell's list: diabetes, kidney disease, an overactive thyroid, pancreatitis, fever, asthma, eye infection, dental disease, dislike of a new food, stress from a change at home, and the loss of a companion cat. It singles out teeth: the pain that comes with dental disease is often the reason a cat refuses to eat.
A full exam, with particular attention to the teeth and gums, then whatever bloodwork or imaging the exam points to. To get food in while the cause is found: syringe feeding, an appetite stimulant such as mirtazapine, or a feeding tube.
A dog is different. A healthy adult dog that skips a meal and is otherwise itself can be watched until the next meal. A dog that skips meals and is also vomiting, flat, in pain or hot is a same-day visit, and so is a puppy or a small breed that stops eating. Loss of appetite is on Merck's list of signs that turn kennel cough into something more, and on the heartworm society's list of early heartworm signs.
Write the date it started and what it turned down, and anything it did eat in the log on My Pet. The vet sheet prints it, and "since Tuesday" beats "recently".
Read 18 September 2026.