Why can’t cats eat onions?

Cats cannot eat onions because onions contain n-propyl disulfide, a compound that damages feline red blood cells and leads to hemolytic anemia. Eating too many onions can even cause fatal poisoning, so the owner must never feed onions to a cat.

If a cat accidentally eats onion, the owner should induce vomiting immediately and give antioxidants such as vitamin E or vitamin C, then provide symptomatic treatment based on the cat’s clinical signs. Generally, if only a small amount was eaten, the cat can be saved in time.