What happens if a dog eats a little bit of onion?

Updated June 6, 2021

Emergency care (details below)

What To Do If A Pet Eats Onion

Toxin absorption can be prevented by immediately seeing a vet to induce vomiting
If onion has been absorbed then daily blood tests are needed to monitor anaemia
Please see a vet even if the amount seems tiny: pets vary in sensitivity and the toxic dose is low

now dive deeper…

Onion ingestion is the third most common poisoning vets see in Adelaide. Like so many pet poisons, onion is a trap we accidentally lay for our pets.

Cooking and leftovers are the problem. Raw onion advertises its toxicity so well that no self-respecting dog or cat would eat it. Add a bit of heat, some other ingredients, and suddenly it’s nice and tasty without the unpleasant warning flavours that keep our pets safe.

How Much Onion Is Dangerous?

For most dogs, as little as 2.5g of onion per kilogram of body weight can produce serious effects. That equals only 15g in a Jack Russell Terrier. Similar results have been observed with garlic, and it’s probably the same for related vegetables.*

Two essential facts:

All dogs who eat onion should be made to vomit as susceptibility varies.
Exposure is cumulative. The lower line on the graph at the top shows how slowly dogs recover. Any more onion in this period will add further damage and increase risk.

*The study (link below) used 5g/kg of dehydrated onion, which is probably equivalent to cooked onion. An equivalent amount of fresh onion would be heavier. Some of the dogs developed life-threatening anaemia so the hazardous dose is clearly lower; I have arbitrarily chosen half.

Is Garlic Toxic To Pets?

Yes. Experience tells us that the entire onion family is dangerous. That includes:

All onion varieties
Garlic
Leeks
Spring onions
Shallots
Even chives

Why Are Onions Poisonous?

Isn’t it strange that humans can happily eat onion but many other animals can’t. The reason is quite unexpected: it’s all about antioxidants.

Onion, whether cooked or raw, contains sulfur compounds that cause oxidative damage. The red blood cell in dogs and cats has a low antioxidant capacity. Put these together and disaster ensues.

That means that when dogs or cats eat onion, the red blood cells undergo chemical attack. Two serious consequences arise:

Haemoglobin (the molecule that carries oxygen) is deactivated
Cell walls are ruptured and red blood cells are destroyed

The result is anaemia and a reduced ability to deliver oxygen to the body.

Symptoms Of Onion Poisoning

Signs of onion poisoning typically appear after 1 to 3 days when the anaemia develops. They include:

Lethargy
Weakness
Laboured breathing
Pale gums
Collapse

You might also notice red urine and yellow eyes from pigments released by the destruction of red blood cells.

Treatment Of Onion Poisoning

Dogs that have eaten onion within the last hour can be treated simply by making them vomit. After this time it’s likely that some will have been absorbed.

If so, vomiting may still be worthwhile followed by a dose of activated charcoal. However, there is no antidote for the toxin that reaches the bloodstream.

These dogs need daily monitoring via blood tests. Some will need oxygen support or transfusions but the good news is that most will recover uneventfully.

Have something to add? Comments are welcome below and will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. The information provided here is not intended to be used as a substitute for going to the vet. If your pet is unwell, please seek veterinary attention.

Note: Dog owners should consult a local vet immediately for any quantity consumed. I am unable to comment further on whether certain amounts are toxic.

Can Dogs Eat Onions?

No, onions are not safe for dogs. In fact, they’re one of the most dangerous human foods out there for our canine companions. It turns out that ingesting too much onion can damage a dog’s red blood cells, possibly leading to a serious medical issue called hemolytic anemia.

All parts of the onion is considered dangerous for dogs which means you should be extra careful when cutting up this vegetable or storing them in a hard-to-reach location in your kitchen. Your dog should not eat the flesh of an onion, leaves, juice, or even powdered version of onion as they all are dangerous for your pets.

Let’s take a closer look at onion toxicity in dogs so that you know what to have your pet avoid, what onion poisoning might look like in your pooch, and what to do if your dog accidentally ingests the dangerous vegetable.

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Why Are Onions Bad for Dogs?

In the case of certain toxic foods for dogs, like grapes, experts don’t know precisely why those foods are harmful. With onions, though, the answer is clear.

Onions contain a chemical that’s toxic for dogs called N-propyl disulfide. This chemical is a sulfur compound, and it’s at the root of why onions are so dangerous for dogs.

N-propyl disulfide attaches to the oxygen molecules of your dog’s red blood cells, causing oxidative damage. This prevents the red blood cells from carrying oxygen properly. That’s harmful enough on its own, but it also tricks your dog’s system into thinking that its own red blood cells are dangerous. In this way, your dog’s body attacks the red blood cells in a process called hemolysis.

Hemolysis, when left unchecked, will lead to hemolytic anemia. This means that your dog’s red blood cells are being destroyed faster than they can be made, leading to serious symptoms of poisoning and even death without treatment.

All Parts of The Onion Are Poisonous For Dogs

Every part of the onion is poisonous, including the leaves, flesh, skin, and even the juice. Also, it doesn’t matter whether the onion is cooked or raw. Cooking an onion does not remove the disulfide chemical, so it’s just as dangerous for your four-legged friend.

It’s important to note that all types of onions are dangerous. White onions, yellow onions, red onions, green onions … none of them are safe for Rover. Additionally, different forms of onions all put your dog at risk. Onion powder is especially dangerous, and other forms — dried or dehydrated, fried, juiced, etc. — put your dog at risk as well.

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Foods Similar To Onions That Can Be Harmful

Onions are a member of the allium family of root vegetables. The alliums include garlic, shallots, leeks, scallions (also known as green onions) and chives. Every one of these vegetables is dangerous for your dog. In fact, garlic has a higher concentration of N-propyl disulfide than regular onions, so it can harm your dog even faster. For this reason it is highly recommended that you keep onions away from your dog and places they may be able to reach.

Keep in mind that many, many foods contain onions, garlic, or onion or garlic powder as an ingredient. Onions are known to be dangerous for many different pets. Onions are even present on a list of what can rabbits eat which helps you know that this vegetable isn’t safe for most pets. Typically when a fruit or vegetable is dangerous for one companion animal it will be dangerous for most of the different types of pets out there. But this rule isn’t always the case which is why it is always recommended to speak with your vet before giving your pet a new type of food or snack.

Your dog might not chow down on an entire onion that fell onto the kitchen floor — although that’s entirely possible — but he or she will definitely go after that tasty onion ring, or a bit of that breakfast quiche. Your dog will typically be interested in new types of foods but you should always be aware of what is safe for them and what isn’t safe for them.

Signs of Onion Toxicity in Dogs

If your dog eats a large number of onions or related foods in a short time, toxicity could set in quickly. But it’s more common that symptoms appear a few days after ingestion.

It’s also possible for N-propyl disulfide to build up in the blood slowly over time, thanks to your dog eating small amounts of allium-family food over an extended period.

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What Are the Symptoms of Onion Toxicity?

If your dog eats onions there is a potential that your dog can get sick. So it is important to know the symptoms of onion toxicity. Symptoms of onion toxicity include:

Lethargy
Loss of appetite
Pale gums
Elevated heart rate and/or respiratory rate
Vomiting
Diarrhea
Ataxia (a lack of coordination)
Discolored urine

Without treatment, a dog suffering from onion poisoning may experience kidney failure or even death.

How Much Onion Can Make a Dog Sick?

Another reason that onions and other alliums are dangerous is because it doesn’t take a lot to cause serious health problems in dogs. Generally speaking, toxicity occurs when a dog ingests more than 0.5% of their body weight in onions at one time.

To put it simply, even a small amount of onion, garlic, or other toxic allium food can poison a dog easily. The smaller the dog, the greater the danger — eating a small bit of onion might not harm a 150-pound mastiff, but it can cause serious health symptoms in a 10-pound dog like a chihuahua. It is important to know what types of human food your dog can safely eat as there are some foods that are beneficial for dogs while there are other human foods that can be dangerous for the health of your dog.

Treatment For A Dog Suffering From Onion Toxicity

If your dog is exhibiting the above symptoms and you know or suspect that he or she has ingested onions or a related food, take them to the vet’s office as soon as you can. Time is of the essence when dealing with any case of poisoning, including onion poisoning.

Diagnosing Onion Poisoning In Dogs

Your veterinarian will diagnose your dog based on a combination of test results, symptoms, and a health history that includes eating onions. Hemolytic anemia is detected with a microscopic test that looks for Heinz bodies on a blood smear. When that test result is combined with known recent onion exposure, onion toxicity can be definitively diagnosed.

Treating Dog Onion Poisoning

Your veterinarian might use a variety of treatments to stabilize your dog and return him or her to full health. The stomach may be flushed to remove the remaining toxin, or vomiting may be induced. Sometimes, activated charcoal is administered to absorb the toxin in the gut. Intravenous fluids may be given to help flush your dog’s bloodstream and maintain proper hydration. Then, your pup will be monitored closely until the body starts producing enough healthy red blood cells again.

In severe cases of onion poisoning, oxygen supplementation and a full blood transfusion may be necessary.

Generally speaking, the outlook is good for a dog who receives early veterinary care. Remember: Time is of the essence, so if you know or even think that your dog may have gotten hold of onions or something containing onions, act quickly. Take them to the vet’s office right away, because it’s always better to be safe than sorry.

What Should I Do If My Dog Eats Onions?

Most dogs will recover from eating small amounts of onions but you should always show extra caution. If your dog eats onions even if it is a small amount it is recommended that you speak with your veterinarian or call a dog toxicity hotline. Your vet will have a better understanding of the current health of your dog and will know how the number of onions they consumed will impact them.

Larger dog breeds will typically be able to digest and recover from eating small amounts of onions better than smaller dog breeds purely based on their size. You should always be mindful of where you store your onions and make sure to keep them away from your dog.

So, Can Dogs Eat Onions? Keeping Your Dog Safe in the Future

Are onions bad for dogs? Yes, they’re one of the most harmful human foods for our four-legged friends. What makes them even more dangerous is the fact that they’re so widespread. You’ll find onions in one form or another in everything from risottos and gravy to tacos and baby food. Plus, it only takes a small amount to make a dog sick.

There’s only one foolproof way to keep your dog safe from onions, garlic, and the other members of the allium family: Tightly restrict your pooch’s access at all times. Pay careful attention when you bring onions home, and when you’re preparing food with onions, garlic, chives, leeks, or shallots, so that your dog can’t eat pieces of these foods or any dishes that contain them. It’s safest to keep your dog out of the kitchen entirely when you’re preparing a meal.

Onions aren’t the only vegetable out there that’s dangerous for our canine friends. In fact, there are many vegetables and fruits that can harm dogs, as well as several that are safe. Make sure to do your research so that you know what you can and can’t give your beloved companion.

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