Many people love onions, and there are plenty of foods that we enjoy that contain them. As always, we must remember that what is great and tasty for us can be extremely harmful for our pets.

Are onions toxic to dogs?

Onions contain a toxic principle known as N-propyl disulfide. This compound causes a breakdown of red blood cells, leading to anemia in dogs.

The toxin causes oxidative damage to your dog's red blood cells by attaching to the oxygen molecules in your dog's red blood cells. This reduces the ability of the red blood cells to carry oxygen, and also tricks your dog's body into thinking that the blood cell is an invader. The red blood cell is destroyed in a process known as hemolysis, resulting in hemolytic anemia.

What parts of onions are toxic to dogs?

All parts of the onion plant are toxic to dogs, including the flesh, leaves, juice, and processed powders. Raw or cooked, fried or powdered, onions and the rest of the allium family (garlic, shallots, leeks, and chives) are harmful to dogs.

Onion powder is in a surprisingly wide range of foods, from soups to baby food. It only takes 100 grams of onion (about the size of a medium onion) per 20 kilograms of a dog's weight to cause toxic effects, which means that a 45-pound dog would only have to eat one medium-to-large-size onion to experience dangerous toxicity levels. Since most dogs would happily devour a bag of unattended onion rings or an onion casserole, given the opportunity, this is a serious concern.

Onion and garlic powders are even more potent than fresh onions. It is always a good idea to check the label of any human food we feed to our dogs, and onion powder should be in your list of “don'ts.” As a word of warning to those with multi-species households, onions are even more toxic to cats than they are to dogs, so keep both feline and canine tummies free of onion treats.

Specific Foods to Think About

Onions are a common ingredient found in many of the foods we eat — including foods you might not consider a danger to your pet. Make sure these foods do not contain any type of onion before you consider letting your pet indulge:

• Pizza

• Tomato sauce

• Chinese food

• Some baby foods

Symptoms of onion toxicity in dogs

If you think your dog may have eaten onions, there are a few symptoms of anemia to look out for:

• Lethargy

• Weakness

• Decreased appetite

• Pale gums

• Fainting

• Reddish urine

The ASPCAalso lists vomiting, elevated heart rate, and pantingas signs of onion toxicity.

Your pet also could lose interest in food as a result of this type of poisoning. It may take up to two to four days after your pet eats the onion for symptoms to appear.

If your dog is exhibiting any of these symptoms, the best thing you can do to help him is to get him to a veterinarian as soon as possible. Your veterinarian will diagnose your dog's condition based on his symptoms and blood work. If your vet detects hemolytic anemia or the formation of Heinz bodies on a blood smear, and that is combined with a recent history of onion exposure, then all signs point toward onion toxicity.

Other conditions can also cause hemolytic anemia, so it is important to get an accurate diagnosis to ensure your dog gets the best care

Onion toxicity can be fatal. The faster you get your dog to the veterinarian, the better her chances, and you can prevent onion poisoning from recurring in the future by keeping onion dishes out of the reach of inquisitive noses.