Can Cats Eat Onions?

Onion toxicity in cats is more severe than in dogs because cats' red blood cells are more susceptible to oxidative damage. The toxic compounds (N-propyl disulfide and other organosulfur compounds) attack hemoglobin, forming Heinz bodies that cause red blood cells to rupture.

The toxic dose for cats is approximately 5 grams of onion per kilogram of body weight — roughly one tablespoon of chopped onion for an average cat. However, toxicity is cumulative: smaller amounts over several days can cause the same damage.

ALL members of the Allium family are toxic: onions, garlic, leeks, chives, shallots, scallions. Garlic is approximately 5 times more toxic than onions. All forms are dangerous — raw, cooked, dehydrated, powdered, in sauces, or in baby food. Onion and garlic powder are especially insidious because they're hidden in many prepared foods.

Symptoms develop gradually over 1-5 days: lethargy, weakness, decreased appetite, pale or yellowish gums (jaundice), dark reddish-brown urine, rapid breathing, and elevated heart rate. By the time symptoms are obvious, significant red blood cell destruction has already occurred.

Common exposure routes in cats: baby food (many brands contain onion powder), table scraps from soup or stew, gravy or sauce drippings, and chives from herb gardens (some cats chew on them like grass).