Can dogs eat onions and garlic?

Allium vegetables contain sulfur compounds that oxidize the hemoglobin in red blood cells. The damaged cells are then destroyed by the body faster than they can be replaced — a process called hemolytic anemia. The oxidative damage begins within a day, but the visible illness is delayed: a dog can seem completely fine for several days after the meal, then become weak and pale as the anemia sets in.

That delay is the trap. Owners often connect the symptoms to something recent rather than to the onion soup or garlic bread from earlier in the week. A single large ingestion is dangerous, and so is a small amount eaten regularly, because the damage accumulates. Watch for tiredness, pale gums, faster breathing, and urine that turns dark or reddish.