Why
Onions belong to the Allium family. The ASPCA says they can cause stomach irritation and red blood cell damage, and that cats are more susceptible than dogs. PetMD warns that regular intake can lead to anemia.
What to do instead
- Avoid onion in any form: raw, cooked, powdered or in sauces and baby food.
Safer swaps from the same group: carrots, cucumbers, green beans.
Warning signs
- Signs may be delayed for days.
- Call your vet if your cat ate onion or a dish made with it.
If your cat ate onions
- Note how much your cat ate and when, and keep any packaging.
- Call your vet, an emergency clinic, ASPCA Animal Poison Control ((888) 426-4435) or the Pet Poison Helpline (855-764-7661).
- Don't make your cat vomit unless a vet tells you to.
Other vegetables: quick answers
| Food | Verdict | Short answer |
|---|---|---|
| Chives | Toxic | No. Chives are an Allium, like onions and garlic. |
| Garlic | Toxic | No. Garlic is in the onion family and is toxic to cats. |
| Leeks | Toxic | No. Leeks are in the onion family and should be kept away from cats. |
| Carrots | Safe | Yes, cooked and cut small. Carrots are one of the vegetables vets list as a safe treat. |
| Cucumbers | Safe | Yes. A few small pieces of washed cucumber are a safe, watery treat. |
| Green beans | Safe | Yes. Plain green beans are on the vet list of safe vegetable treats. |
Rules for any new food
- Plain is the rule: no salt, butter, oil, onion, garlic, sugar or sweeteners. Most of the danger in human food comes from what is added to it.
- Keep all treats under 10% of your cat's daily calories . The rest should come from a complete cat food.
- Check labels for onion and garlic powder, which turn up in stock, gravy, baby food and seasoned meat.
- If your cat has a health condition, such as diabetes, kidney disease or a sensitive stomach, ask your vet before adding any new food.
Frequently asked questions
Are onions safe for cats?
No. Onions damage cats' red blood cells and can cause anemia.
What should I do if my cat ate onions?
Call your vet, an emergency clinic, or ASPCA Animal Poison Control at (888) 426-4435 right away. Note how much your cat ate and when.
Sources
- ASPCA Animal Poison Control, "People Foods to Avoid Feeding Your Pets"
- PetMD, "Human Foods That Are Dangerous for Cats" (reviewed by Nicole Silva, DVM)
- VCA Animal Hospitals, "Can You Feed Pets Certain Fruits and Veggies?"
Checked October 17, 2026. We are a reference, not a vet: if in doubt, call yours. How we check.