The onion (Allium cepa
) is a perennial bulb plant used as a crop plant worldwide. They are used in many dishes for flavor and health benefits for humans. Onions contain many types of flavonoids, allyl cysteine sulphoxides, aliphatic sulfides, and relatively rare amino acids S-meth and S-prop ylcysteine sufoxides (SMCO). It is n-propyl disulphide which is the principal chemical which can potentially be toxic to birds. If ingested in large enough quantities (more then 0.5% of their body weight), onions can damage red blood cells and cause heinz body anemia. The reason why humans aren't affected, is because they are the most resistant species studied.
All forms of onion are potentially toxic--dehydrated, cooked, powder, raw and includes garlic, leeks, shallots, and other plants of the Allium