Onions damage the red blood cells in dogs and are not safe for them to consume. All foods in the onion family, such as shallots and scallions, are toxic to dogs.
Shortly after consuming onions, dogs may appear lethargic, weak or have trouble breathing. Other symptoms of onion consumption in dogs includes vomiting, dark urine and yellowed gums or eyes. Dogs that have consumed onions need to be taken to a veterinarian as quickly as possible. While certain dogs may not need extensive treatment after consuming onions, severe cases may require a blood transfusion and close monitoring for several days.