Onion Toxicity in Dogs and Cats

Onions. Getty - PhotoAlto Agency RF Collections/Laurence Mouton

Not all of the toxic foods are 'icky,' raisins and grapes, yeast dough, and as many people know, chocolate, all pose a risk to dogs. Here is another human food to add to the list: onions.

Clinical Presentation:

A terrier comes into the office with severe respiratory distress, panting heavily and laying down. A laboratory test shows the patient has a dangerously low level of red blood cells, and an immediate transfusion is necessary.

After talking with the owner, it appears the problem began after the dog got into the kitchen garbage. Review of a blood smear reveals changes to the shape of the red blood cells consistent with oxidative damage.


An acute toxic reaction to eating onions.

Everyday Toxins

Many owners are not aware that several common foods and chemicals can cause this type of life-threatening reaction. Tylenol and the zinc in pennies can also cause severe distress and this type of oxidative damage in puppies and smaller dogs, such as a Maltese, Yorkshire or Jack Russell.

Dogs over 20 pounds often consume similar substances, but their larger mass usually prevents such a severe reaction.

Signs of Onion Toxicity in Pets

Common Signs:

  • Lethargy
  • Trouble breathing
  • Vomiting
  • Dark-colored urine
  • Yellow gums and whites of eyes

The chemicals found in cooked, raw or dehydrated onions begin reacting with a dog's metabolism soon after consumption, preventing the red blood cells from carrying oxygen to the body. Within a few hours, the patient becomes lethargic and has trouble breathing. Other clinical signs may include dark-colored urine or a yellowing of the gums (called icterus). The patient may also vomit up the onions or other foods consumed from the trash.

Treatment of Onion Toxicity

After the patient is brought to the hospital, the lab tests show the patient is anemic and there are changes to the red blood cells that characterize this type of toxic reaction. Depending on the patient's condition, a blood transfusion may be necessary until the toxic chemicals can gradually be metabolized.

Metabolism of the toxin is rapid in dogs, but the damaged red blood cells may take 2 to 3 days to be removed from circulation. Typically, patients who are monitored closely and receive the right support, including blood transfusion(s) and intravenous fluids, make a quick recovery and can go home after a day or two (or 3) at the hospital.

Possible Complications

It is important to watch the patient for other signs of distress, such as gastritis, diarrhea or pancreatitis, especially when fatty foods from the trash have been consumed along with the onions.

In any case, knowing what foods or substances the patient ate in the house, the trash or in the yard, can help the veterinary specialist determine the nature of the problem and the best way to treat the condition.

A Note About Cats and Onions

Cats are much more susceptible to this kind of anemia, but their more discriminate taste typically keeps them away from onions. Cat exposure to this problem is sometimes seen when being fed baby foods containing onion powder. People often reach for baby foods when their cat is not eating well, or as a "treat." Therefore, it is important for the owner to look at the ingredients label before offering.