- All forms count - even powdered
- Often delayed 1+ day
- Affects: Red blood cells
Why this verdict for cats
Cats are even more sensitive than dogs to onion toxicity, which destroys red blood cells.
Warning signs to watch for
- Weakness
- Pale gums
⚠ If your cat ate onion
Act immediately — don't wait for symptoms.
- Call your vet or a pet poison helpline right away.
- Note how much was eaten and when.
- Do not induce vomiting unless a professional tells you to.
Onions — raw, cooked, fried, powdered or dehydrated — are toxic to dogs and cats because they damage red blood cells and can cause anemia.
How much is safe?
All forms count and the effect is cumulative. The sneakiest sources are concentrated: onion powder and dehydrated onion in soups, gravies, baby food and seasoning blends pack far more punch than a slice of raw onion. As a rough guide, problems can begin around 5 grams of onion per kilo of body weight.
What happens if a cat eats too much?
Signs are often delayed by a day or more: weakness, lethargy, pale or yellowish gums, rapid breathing, and reddish-brown urine as red blood cells break down.
⚠ What to do if your cat ate onion
Call your vet or a poison line (ASPCA 888-426-4435 · Pet Poison Helpline 855-764-7661). Because signs can lag, don't wait to see how your pet does — say exactly what and how much was eaten.
⚠️ Worried your pet got into this?
Frequently asked questions
Is cooked onion safe for dogs?
No. Cooking doesn't remove the compound that damages red blood cells — cooked, fried and caramelized onion are all toxic.
What about onion powder?
It's actually more dangerous — it's concentrated, so a small amount in seasoning or soup can deliver a big dose.
My dog licked a little food with onion — is that an emergency?
A tiny one-off taste may be low-risk, but because it's dose-dependent and cumulative, check with a poison line using your dog's weight.
More vegetables for cats
By the CanMyPet Editorial Team · Reviewed against ASPCA Animal Poison Control, the American Kennel Club (AKC) and Pet Poison Helpline · Last updated July 31, 2026.
Sources
- ASPCA — People Foods to Avoid Feeding Your Pets
- American Kennel Club — Dog Nutrition
- Pet Poison Helpline — Poison List