Can Cats Eat Onions? No — They Damage Red Blood Cells

Why onions are toxic to cats

Onions belong to the Allium family, along with garlic, chives and leeks. The ASPCA names N-propyl disulfide as the toxic principle in onion. It damages the red blood cells that carry oxygen, which the body then breaks down faster than it can replace them.

The result is hemolytic anemia, sometimes called Heinz body anemia. The ASPCA's people-food guidance warns that Allium vegetables cause stomach irritation and red blood cell damage that can lead to anemia, and cats are more sensitive to this than dogs.

Hidden onion in everyday foods

Few cats eat a raw onion, so most exposures come from food that does not look like onion. Gravy, soups, stews, meatloaf, burgers, pizza, salsa, stuffing, baby food and broth often contain onion or onion powder, which concentrates the toxin.

This matters at holidays and on busy kitchen counters. Leftover stuffing or a plate of gravy-covered turkey is a classic route. Read labels before sharing anything, and remember that a dish can be dangerous even when you have picked the onion pieces out.

A feeding mat under a ceramic bowl keeps any shared food in one place and easy to clean up.

My cat ate onion: what to do

Work out what was eaten and roughly how much, keep the packaging or recipe, and call your vet or a poison line straight away. Do not make your cat vomit at home unless you are told to, and do not wait for signs before calling.

Onion damage often takes a few days to show, so a cat that looks fine on day one can become ill later. Your vet may recommend inducing vomiting at the clinic, giving medicine to limit absorption, blood tests to check red cells, or monitoring over several days.

Is any amount of onion safe for cats?

No. There is no safe amount to share, and the effect can build up when small amounts are eaten repeatedly, such as onion-seasoned food or broth given day after day. Kittens, small cats and cats with existing illness are especially vulnerable.

Never use human soups, gravies or baby food to tempt a sick cat unless you have checked they contain no onion or garlic. If you have been doing so, tell your vet, even if your cat seems well.

Kittens and onions

Kittens have smaller blood volumes, so the same amount of onion causes a bigger drop in healthy red blood cells. They also explore food left on counters and tables, and may lick gravy from plates or pans.

Keep cooking scraps and leftovers covered and out of reach, and never feed a kitten from your plate. If a kitten ate any onion-containing food, call your vet the same day rather than waiting to see if it gets sick.

Signs of onion poisoning and when to call a vet

Early signs, often within a day, can include vomiting, drooling, diarrhea and reduced appetite. As anemia develops over the next few days, the ASPCA lists weakness, an elevated heart rate, panting and blood in the urine, and you may see pale gums, lethargy or reddish-brown urine.

Go to a vet straight away if your cat has pale or yellowish gums, is breathing fast or with an open mouth, is weak or collapses, or has dark urine. Breathing changes in a cat are always urgent. A cat that ate onion and seems fine still needs a call for advice.

Safe ways to share food with your cat

Keep people-food treats simple and unseasoned: a small piece of plain cooked chicken or turkey, a flake of plain cooked fish or a little plain cooked egg. Cornell's Feline Health Center suggests treats stay under 10 to 15 percent of daily calories.

When you cook, set aside your cat's portion of meat before any onion, garlic or seasoning goes in. That simple habit removes almost all of the risk.

This page is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your pet.