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Why Dogs Can’t Eat Onions (Vet-Approved)

Most owners share their meals and snacks with their pets at some point. Although we do this with good intentions, not every food item is suitable for your dog and some can even be toxic.

While most owners are aware of the toxicity of foods such as chocolate and grapes, not every dog owner realizes that onion can pose a real danger to their pet.

Onions are present in a range of foods that we eat including curries, sauces, dips, stews, gravies, soups, and burgers. We may not even be aware that the food we are sharing contains onion. This is why checking the label is always key before offering your dog a snack. It is also one of the many reasons why fast food and takeaways should never be shared.


Why Can’t Dogs Eat Onions?

Onion, along with other members of the Allium family, such as scallions, chives, and garlic is not something that dogs have evolved to be able to digest and eat. Onion can be toxic in high doses and cause red blood cells to break down.

The problem with onion:

Onions contain a component known as N-propyl disulfide, an oxidative agent which causes red blood cells to break down, resulting in a condition known as Heinz body anemia.

The oxidant level within the cell becomes overwhelmingly high and the antioxidant ability of the cell is exceeded. It is the red blood cell membrane itself that becomes fragile, ultimately leading to cell breakdown and destruction.

A lack of red blood cells can lead to low blood oxygen levels, lethargy, and even death in severe cases.

All dogs are susceptible to onions but some breeds are thought to be more at risk. This includes the Shiba Inu and the Akita.

Vca Hospitals Additiona Research

How Much Onion Is Bad/Toxic For a Dog?

The interesting thing about onion toxicity is that it tends to be something we see after long-term exposure to onion.

A good example is if an owner decides to feed their dog a home-cooked diet and includes onion in the recipe. In this case, the negative effects of the onion won’t appear on the first or second day, but over time the onions will have a negative impact and make the dog unwell. 

Depending on the size of your dog, a single onion can cause immediate signs of toxicity. We know that the toxic dose is about 100 grams of onion per 20kg (dogs weight).

For example:
If you have a 15kg beagle, it would take just 75 grams of onion (one small onion) to be a toxic dose.

Typical weight of one onion:
Large onion: 220-280 grams
Medium onion: 140-180 grams
Small onion: 90-130 grams

While it would be unusual for an owner to actually give their dog a whole onion, the dog may steal it from the kitchen or garden, unaware of how ill it will make them.

Certain “greedy” breeds such as Labs and Beagles are notorious for food stealing but any dog is capable of committing such an offense.

Curious puppies and dogs with an increased appetite due to an illness or medicine they are taken, are the most common offenders.

Interesting: My Dog Ate Spaghetti Sauce (why this is very bad)

Will a Little Bit of Onion Cause Harm To My Dog?

As discussed, the damage done by the onion is both breed and dose-dependent. It is also known that certain genetic disorders and medicines can make a dog less tolerant of the Allium species.

The average dog can tolerate a small amount of onion with no ill effect. A one-off small amount of onion will not harm your dog. Prolonged consumption of large amounts of onion is more of a problem.

In fact, many owners are completely unaware of the dangers of onion and may feed it to their dog on occasion, with no repercussions.

However, most vets advise avoiding onion completely as it is simply not worth the risk. Dogs do not need to eat onion to have a balanced diet and it offers them no real benefits. Onions are dangerous whether given cooked, raw or powdered.

So if you’re asking this question because your dog has snaffled a small piece of chopped onion from the ground while you were preparing dinner, there is no reason to be concerned.

As an emergency vet, I would get plenty of calls from worried pet parents whose toddlers had just thrown a small chunk of onion on the ground, only for the family dog to have hoovered it up. A small exposure like this is nothing to get worked up about.

What To Do If My Dog Eats Onion?

If your dog has eaten a large amount of onion or has been eating onion over time and seems unwell, the best place for them is your local veterinary clinic. 

Acute onion poisoning needs to be treated immediately. The sooner your dog is seen, the better its prognosis.

If seen within a few hours of eating the onion, the vet will induce vomiting and start activated charcoal meals and intravenous fluids to minimize toxin absorption. This is done in an attempt to prevent severe anemia.

Remember, right after eating onion, your dog may seem clinically normal. But this is not a reason to keep them at home.

If you’ve fed your dog onion recently and are concerned they may have been poisoned here are the signs to watch out for:

  • Gastrointestinal signs such as vomiting and diarrhoea
  • Nausea
  • Abdominal pain
  • Pale gums
  • Lethargy
  • Fast breathing
  • Rapid heartbeat
  • Weakness
  • Collapse
  • Some owners have reported they could smell a bad “onion breath smell” coming from their dog. While not all dogs are likely to exhibit this sign, it could prove useful in cases of toxicity where the owner is unsure if there has been onion ingestion or not.

When To Seek Help From a Vet

So if your dog has eaten onion, when should you seek veterinary help? Let’s cover this in detail.

First thing to do:
Decipher roughly how much was eaten, over-estimating if unsure. If there is a chance they have consumed a toxic amount, you need to bring them to a vet right away. (Toxic amount being 100grams per 20kg (dog weight)

If you are aware your dog has been eating onion for a prolonged period of time (accidentally incorporating it into their diet) then you should have a vet perform a full health exam

Related: Why Dog’s Can’t Eat Nature Valley Bars.

The importantance of treatment:
Heinz body anemia is not a condition that can be treated at home, so vet treatment is key. Delaying treatment can result in further anemia and dogs can go on to develop kidney failure and trouble breathing.

Vets will examine your dog and take a blood sample and urine sample to analyze. They will be checking for a low red blood cell count and telltale markers of Heinz body anemia. Heinz bodies should not normally be seen in dog blood and can be picked up on a blood film exam. Your dog may have further testing such as measurement of their oxygen saturation, urine analysis, and cultures for infection.

Importantly, if the onion was recently ingested, bloodwork may initially seem normal. Very high doses can lead to anemia in as little as 24 hours, but it is not uncommon for bloodwork to remain normal for 2-3 days despite the poisoning.

This is why re-testing in a few days should be done, to check if the red cells have suffered any damage.

Those pets who do have dangerously low red cell levels may require hospitalization, intravenous fluid therapy, a blood transfusion, and supplemental oxygen. There is no specific antidote for onion poisoning.

Supportive care is all that is needed as the dog’s own bone marrow should produce new red blood cells within a few days. As long as there is no further onion exposure, the patient should go on to make a full recovery and should suffer no long-term effects.

Recovering From Onion Poisining (General Advice)

Those who are well enough will be sent home to recover. Your vet will have given you specific instructions in relation to exercising your dog and taking care of them.

Most patients require a period of rest and will be less able to cope with vigorous exercise for some time. Let your dog take it easy, especially in the first week or two.

Be sure to pinpoint where your dog accessed the onion and to take steps to prevent it from happening again.

This may mean getting a lock for the pantry, fencing off your vegetable patch, or changing your food sharing habits.

Similarly, keep your dog away from related vegetables including garlic, chives, scallion, and leeks. Of all the Allium species, garlic is the most ‘potent’ and can cause adverse effects at relatively small doses.

Be wary of “natural” products that contain onion and claim to be endorsed by vets. Some nutraceuticals, supplements, and other canine-specific products may contain onion and should never be given to a dog, regardless of what the compelling advertisement may tell you to do. Always consult your vet before giving your dog any new product.

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Additional Research: US National Library of Medicine National Institutes of Health


Before making any decisions that could affect the health and/or safety of your dog, you should always consult a trained veterinarian in your local area. Even though this content may have been written/reviewed by a trained veterinarian, our advice to you is to always consult your own local veterinarian in person. Please read our full dislcaimer if you have any questions.