Onions and all Allium family plants (garlic, leeks, chives) are toxic to cats, causing hemolytic anemia by destroying red blood cells. Cats are actually more sensitive than dogs to Allium toxicity. All forms are dangerous — raw, cooked, powdered, and dehydrated.
Why Is This Toxic to Cats?
The organosulfide compounds in onions oxidize feline red blood cells, creating Heinz bodies. These damaged cells are destroyed by the spleen, causing life-threatening anemia that can develop over days.
Because many commercial cat foods and broths contain trace amounts of onion or garlic powder, cumulative exposure over time is also a concern. Check ingredient labels on treats.
| Form | Toxicity to Cats | Toxic Threshold | Risk Level |
|---|---|---|---|
| Onion Powder | Highest | 0.5g/kg body weight | EXTREME |
| Raw/Cooked Onion | High | ~5g/kg | HIGH |
| Garlic (any form) | 5× higher than onion | Lower threshold | EXTREME |
| Baby food with onion | Hidden source | Cumulative risk | HIGH |
Symptoms & Timeline
GI Upset
Vomiting, diarrhea. Anemia not yet visible.
Anemia Developing
Weakness, pale gums as red blood cells are destroyed.
Severe Anemia
Collapse risk. Immediate veterinary care critical.
Recovery or Crisis
Blood transfusion may be needed. Fatal without treatment.
🚨 What To Do Right Now
Anemia develops over days — even if your cat seems OK now, contact your vet immediately.
Frequently Asked Questions
Yes. Cats appear to be more sensitive to Allium toxicity than dogs, with a lower toxic threshold relative to body weight.
No. There is no safe amount. Even trace amounts in cat food over time can be harmful.
Onion powder is 3–5× more concentrated than fresh onion. Call Poison Control immediately.
GI symptoms appear within hours, but anemia — the most dangerous effect — develops over 1–5 days.
Yes. Garlic is approximately 5× more toxic than onion by weight for cats.