Can Cats Eat Onions?

You can add onions to the list of foods you should never feed your cat.

“Cats are extremely sensitive to onions,” Dr. Sarah Wooten, a small animal veterinarian in Colorado, told The Dodo.

Even a small amount can be toxic.

If your cat has eaten something with onion in it, take him to the vet ASAP. But if you’re only thinking about sharing your onion bagel or onion powder-seasoned eggs with your cat, put it down and read this instead.

Onions contain a compound called thiosulphate that is extremely dangerous for cats (and dogs). It can break down a cat’s red blood cells to the point of anemia (aka a lack of blood cells).

“Anemia means there are not enough red blood cells to supply oxygen to all the cells of the body,” Dr. Hanie Elfenbein, a veterinarian at the Humane Educational Society in Tennessee, told The Dodo. This ultimately leads to a whole mess of symptoms, and a very sick cat.

Both onions and garlic contain thiosulphate and should be avoided at all costs. This goes for any vegetable in the allium family, which includes shallots, scallions, leeks and chives (so avoid these, too!).

Onions in any form can be toxic for cats. Onion powder, onion salts, cooked onion and dried onion can all cause serious problems. Even a small bit of onion in broth is harmful, and your cat should steer clear of it.

According to Dr. Wooten, it only takes about 5 grams of onion per kilogram of body weight for your cat to start having symptoms.

For a 10-pound cat, this would just be a couple slices of onion.

But that doesn’t mean it’s OK to feed him a smaller bite. Since onions can be so dangerous and every cat reacts differently, it’s very important to avoid onions altogether.

“Not all cats react to eating onions in the same way. That is why if you know your cat ate onion it is important to bring him to the veterinarian right away,” Dr. Elfenbein said.

Here are common signs of onion toxicity in cats:

“If your cat eats onion he may first develop a very bad stomach ache, as the onion causes damage to the stomach and intestines,” Dr. Elfenbein said. “He may vomit and develop diarrhea. Next, over several days he will become pale, lethargic and weak. This weakness is due to severe anemia.”

In extreme cases, when the cat has eaten a lot of onion, a side effect can be kidney damage.

Unfortunately, there’s no quick treatment for onion toxicity in cats — which is another reason why it’s so important that your cat never eats onions.

If you take your cat to the veterinarian for onion toxicity, it’s likely your cat will be hospitalized and given intravenous fluid therapy (aka an IV) to flush the body of the toxin. This process can take a few hours to several days. “Treatment is expensive, as it requires multiple days of IV fluids in the hospital and possibly one or more blood transfusions,” Dr. Elfenbein said.

Luckily, most cats won’t seek out onions as a treat. The biggest problem occurs when cat parents share food that was cooked with onions or seasoned with onion powder.

Before feeding your cat human foods like chicken or beef broth, pizza, tomato sauce, tuna salad, baby food or takeout, make sure they weren’t prepared with onions (or better yet — have your cat avoid them altogether).

Also, be wary when cooking with onions in the kitchen. “While the tiny piece of minced onion that falls off your cutting board is unlikely to cause a problem for your cat, it is still recommended to keep your cat out of the kitchen while cooking and clean up all pieces of onion immediately,” Dr. Elfenbein said.

Most importantly — if you think your cat has eaten onion, call the ASPCA Animal Poison Control hotline at (888) 426-4435 or bring your cat to the vet right away!