Vomiting is the complaint cat owners bring us most often. Most episodes are harmless. The difficulty is that the harmless ones and the serious ones look identical in the first hour, so it helps to know which details actually matter.

Vomiting that is usually not serious

A cat that brings up a hairball every few weeks, eats normally afterwards and is otherwise bright is generally fine. So is a cat that eats too fast and returns undigested food shortly afterwards; the food comes back in a tube shape, barely changed, and the cat is hungry again straight away.

Both of these are worth mentioning at the next check up, but neither is an emergency.

Vomiting that needs attention

Ask yourself three questions: how often, how the cat is between episodes, and what is coming up.

How often. Vomiting more than once or twice a month is not normal, whatever the cause. Several times in one day is a reason to be seen.

How the cat is in between. A cat that vomits once and then eats, drinks and behaves normally is in a different position from one that hides, refuses food or sits hunched over.

What comes up. Yellow or green fluid is bile. Anything that looks like coffee grounds is digested blood. Fresh red blood, faecal smell, or repeated retching that brings up nothing at all all need to be seen.

What causes it

Hairballs and eating too quickly are the common benign causes. Beyond those: a sudden change of food, food intolerance, intestinal worms, foreign bodies, inflammatory bowel disease, pancreatitis, kidney failure, liver disease, hyperthyroidism, and poisoning.

The important point is that most of these cannot be told apart on the vomiting alone. That is what the examination and blood testing are for.

String is a particular danger

Cats swallow thread, tinsel and elastic more often than any other object. A length of string can anchor at the base of the tongue while the rest travels on, and the intestine then bunches along it and can be cut through. This is a surgical emergency.

If you have seen your cat playing with thread and it is now vomiting, say so when you call. And if you can see string at the mouth or the anus, do not pull it.

What to do at home

Remove food for a few hours, but leave water available. Then offer a small amount of a bland food and see whether it stays down. Do not fast a cat for longer than that: cats that go without food for more than a day or two are at risk of hepatic lipidosis, a liver condition that can be fatal.

Do not give human anti-sickness or painkilling medication. Do not give milk.

When to call

Come in the same day if the vomiting repeats, if there is blood, if your cat will not drink, if it is lethargic or painful, if the abdomen looks swollen, or if you think something has been swallowed. Kittens and older cats dehydrate quickly, so leave less time before calling.