Is Onion toxic to dogs or cats?

Onions contain thiosulfates and organosulfur compounds that damage red blood cells, causing haemolytic anaemia. Cooked onions are equally toxic. Onion powder is particularly concentrated and dangerous. Threshold approximately 0.5% of body weight, but smaller exposures cumulatively cause harm.

Toxicity is dose-dependent. Your dog's weight and the quantity consumed are both important - include these when you call poison control.

Cats are actually more sensitive to onion toxicity than dogs due to differences in their red blood cell structure. Even small amounts from shared human food can cause serious anaemia.