Pets and Onions

Each Layer Can Poison Your Pets

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.

Onions contain compounds called disulfides and thiosulphates which can be toxic cats and dogs if ingested. The ingestion of onions causes conditions called hemolytic anemia, Heinz body anemia, and methemoglobinemia which are all manifestation of damage to red blood cells. Essentially, the compounds in onion can cause the red blood cells circulating through your pet’s body to become very fragile and burst.

Symptoms of this condition include early-onset vomiting and diarrhea, along with symptoms of anemia--breathlessness, lethargy, pale, yellow, or “muddy” colored gums, rapid breathing, and an elevated heart rate. Your pet also could develop abdominal pain and discolored urine. While vomiting and diarrhea may occur within one day, it may take several days to a week after your pet eats onions for symptoms of anemia to appear.

Are All Onions Dangerous To Pets?

All onions — whether cooked or raw or even free-dried — are a danger to your pet. It takes a small amount of onions to poison your cat or dog, with cats being more sensitive to onion's effect than dogs. Additionally, Japanese breed dogs (e.g. Akita, Shiba Inu, Japanese Chin) may be genetically more susceptible than other dog breeds.

Consumption of as little as 5 g/kg of onions in cats or 15 to 30 g/kg in dogs has resulted in clinically important red blood cell damage. Onion toxicosis is consistently noted in animals that ingest more than 0.5% of their body weight in onions at one time.*

Please note that a pet's weight, breed, and prior health history can vary the toxicity level of ingested onion. If you suspect your pet has consumed some type of onion, call Pet Poison Helpline at 855-289-0358** or your veterinarian immediately.

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

"Onion toxicity can be very serious and expensive to treat,” says Dr. Tina Swan, a veterinarian on staff with Nationwide pet insurance.

Swan, who specializes in animal emergency care, recalls diagnosing a patient with food toxicity symptoms. “I had a young dog with signs of partial paralysis and weakness of his back legs,” she says. “The clue to the problem was that the owner had fed the dog some macadamia-crusted salmon with sauteed onions the night before. It can be difficult to determine what causes a toxic reaction in pets, especially if they've eaten table scraps.” 

The best way to avoid accidentally poisoning your pet? Swan always advises clients not to feed their pets table scraps. “Many sources of onion (cooked or raw) have the potential to cause toxicity in pets including onion powder which is in many foods in varying amounts. Although it does take a certain amount to cause a problem, this can be hard to gauge in table scraps.”

What to Do If Your Pet Is Poisoned

If you suspect your pet has consumed some type of onion, call Pet Poison Helpline or your veterinarian immediately. The condition can be treated, but it’s important to seek medical attention as early as possible to prevent damage to your pet’s red cells. Always keep an emergency veterinary clinic phone number and address handy in case your veterinarian is not available.

The condition, if severe, can require significant hospital time and in extreme cases a blood transfusion might be necessary.

Want to learn more about toxic foods for pets? Read about chocolate toxicity and raisin and grape toxicity.

**A per case fee is billed by Pet Poison Helpline. PPH is not affiliated with Nationwide pet insurance .

*Smith K and Schildt J. Onions and Garlic. In Hovda LR, Brutlag AG, Poppenga RH, Peterson, KL eds. Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Small Animal Toxicology. 2nd ed. Ames, IA: Wiley-Blackwell, 2016.