Vegetables
Can cats eat onions?
Onions damage red blood cells in cats and can cause anaemia — even as powder.
Portion: None.
The short answer
No. Onions are toxic to cats in every form — raw, cooked, powdered, dehydrated or hidden in sauces, soups and baby food. Cats are particularly sensitive to the compounds in allium plants, which damage red blood cells. Signs can appear days after eating, so contact your vet promptly if your cat has had any onion.
Why it’s dangerous
Onions contain organosulfur compounds (such as n-propyl disulfide) that oxidise haemoglobin, forming Heinz bodies. Damaged red blood cells are destroyed, causing haemolytic anaemia. Cats' haemoglobin is especially prone to oxidative damage, making them more sensitive than dogs. Cooking does not destroy these compounds.
How to keep your cat safe
- Never feed onion in any form.
- Check labels: onion powder is common in broths, gravies, baby food and deli meats.
- Keep leftover takeaway and stir-fries away from cats.
Signs of trouble
- Lethargy and weakness
- Pale gums
- Rapid breathing or heart rate
- Red-brown urine
- Vomiting, drooling, loss of appetite
Onions & cats: FAQ
How much onion is toxic to a cat?
Very little — the Merck Veterinary Manual notes cats can be affected at around 5 g/kg of onion, and repeated small amounts add up. Don't wait for symptoms.
Is cooked onion safe?
No. Cooking does not remove the toxic compounds.
Can cats eat food cooked with onion powder?
No. Powders are concentrated and a common hidden source of poisoning.
Related foods
See every food that’s toxic to cats →
Sources
- Merck Veterinary Manual — Allium Species Poisoning in Animals (accessed 2026-09-29)
- ASPCA Animal Poison Control — People Foods to Avoid Feeding Your Pets (accessed 2026-09-29)
Last updated 2026-09-29. We are not veterinarians: this guide summarises published veterinary references and is not a substitute for advice from your vet. See our methodology and disclaimer.