Is It Really Dangerous for Cats to Eat Onions?

Posted on 12 Mar 2018 21:48 by EricT


My little cat Petey loves these turkey 'snack sticks' I keep around. He isn't generally crazy about people food but he is obsessed with these things. Problem is, they are basically sausages, something you should avoid giving to cats. There may be all sorts of things in sausage that could be bad for your cat, but specifically, I'm afraid of the potential presence of onions or other allium vegetables.

Onions and garlic can be so dangerous for cats or dogs that the effects have a special name, onion or garlic toxicosis. Any plant in the genus allium could be dangerous, including onions, garlic, leeks, shallots, scallions, and chives, but will stick to the term onion toxicosis for convenience.

Onion toxicosis is much more common in dogs than cats, but that is simply because cats are more finicky eaters. Your cat isn't likely to munch on some raw onion. However, any food that your cat enjoys regularly and which contains these alliums in any form, including onion or garlic powder, could cause certain compounds to build up in their body and lead to toxicosis. Baby food, which may contain onions or garlic, may be a particular problem for cats. And, remember, some cats aren't so discerning. My other cat, Miranda, is a chow-hound and loves everything, including such things as tomato sauce containing onions.

Now, if your cat eats a little bit of an onion-containing food, now and again, you do not need to panic. It's going to take a lot and, usually, regular exposure to onions or other alliums over a longer period of time. Dog owners need to be much more vigilant since dogs are much more likely to get into food they should be eating. So, for cats, just be careful and avoid exposing your cat to anything that you know contains, or which has the potential to contain onions.

Onions and other allium vegetables are dangerous for cats and dogs to eat.
Onions and other allium vegetables are dangerous for cats and dogs to eat.

Why are Onions Dangerous to Cats?

Onions and other alliums contain sulfoxides. These compounds are what give the vegetables their characteristic odor. They hydrolize to thiosulfinates which become dipropyl sulfides. These compounds affect the red blood cell membranes of cats (and dogs) by oxidizing them, this can cause the cells to rupture and thus be destroyed, leading to anemia. Also possible is the formation of clumps of denatured hemoglobin within the cells called Heinz bodies. And, more rarely, methemoglobinemia.

Does Cooking the Onion Help?

Cooking onions, garlic, etc. has no effect on the principles which cause toxicosis. As well, and as mentioned, drying does not help. Onion or garlic powder is just as problematic as raw onions or garlic.

What are the Symptoms of Onion Poisoning in Cats?

The common signs of onion poisoning, or toxicosis, are:

  • weakness and lethargy
  • pale mucous membranes
  • discolored urine

More rare signs are:

  • bad breath
  • hypersalivation
  • vomiting and/or diarrhea


Treatment for onion toxicosis would depend on whether your pet showed clinical signs, which can take a while to manifest. If you know your cat or dog (most likely dog) ingested a large amount of onions or other alliums, you should immediately go to your vet. They will likely induce vomiting and give your cat a solution of activated charcoal to absorb the poisonous compounds. Your vet would then observe your pet for clinical signs.

If symptoms have occurred, and your veterinary doctor diagnoses your pet with onion toxicosis, which would involve ruling out other diagnoses and performing blood and urine tests, the treatment would be more aggressive. Your pet may receive a blood transfusion, IV fluids, and medication to manage vomiting and diarrhea if needed. Although the precise details can be more complexed, owing to the possible complications of treatment, with prompt care, recovery can be expected. There are possible complications of severe cases of anemia and/or secondary renal damage, but, in general, the prognosis is good.

I'd like you to keep in mind that this article is meant as nothing more than a general overview of the question posed in the title and of the medical condition of onion toxicosis. It should not be considered a substitute for professional veterinary advice. Please consult your veterinary professional should you have concerns or would like more detailed information on the dangers of onions and certain other foods for your cat.

1. Côté, Etienne. Clinical Veterinary Advisor for Dogs and Cats. Mosby Elsevier, 2007.

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