Will A Small Amount Of Onion Hurt My Dog?



will a small amount of onion hurt my dog

Will a small amount of onion hurt my dog? Onion is a staple ingredient in our home, and my pup is also a homing missile to food dropped on the sidewalk. So it feels like the likelihood of him one day ingesting a small helping of onion by accident is pretty high, even though we’re obviously making our best effort to stop him. Luckily, small traces of onion aren’t always toxic to dogs. But there’s no exact science for determining a toxic dose. Here’s how you can judge whether a small amount of onion is likely to harm your dog. And what you should do if you suspect they’ve eaten either a non-toxic, or borderline toxic quantity.


What makes onion poisonous to dogs?

The humble onion is a staple of human diets all around the world. But it’s famously one of the toxic foods that dogs should not eat. Onions contain several naturally-occurring, sulfur-containing compounds, including a family of chemicals called thiosulfinates. Thiosulfinates decompose into disulfides, and when disulfides enter a dog’s bloodstream they bind to the surface of red blood cells, causing the cell surface to break down and the cells to disintegrate.

Without enough intact and functioning red blood cells, it is called anemia, or being anemic. Anemic dogs can’t transport sufficient oxygen from their lungs to the other parts of their body. So they get sick. In extreme cases, severe or prolonged anemia can be fatal.

will a small amount of onion hurt my dog

How much onion do dogs need to eat to be poisoned?

Onion is so ubiquitous in our own diets that it’s not unusual for dogs to get hold of small quantities by accident. Whether from food scraps left on tables, raiding trash cans, or from food scavenged on the sidewalk. Since all parts of the onion plant are toxic to dogs, dogs can also ingest the leaves of onions grown in vegetable gardens or wild onions growing, well, wildly. The Veterinary Poisons Information Service has recorded cases of dogs being poisoned by ingesting red and white onions (cooked and raw), spring onions, and even onion soufflè.

Studies of onion toxicity have revealed that it actually takes a fairly large portion of onions to trigger symptoms of poisoning in dogs. As a rule of thumb, it’s thought that eating a quantity of onions equal to less than 0.5% of a dog’s body weight won’t usually result in signs of harm. This is roughly equivalent to one whole cup of diced onion, or one large-ish whole onion for an average sized Labrador Retriever weighing 60-70lbs.

However, this doesn’t mean it’s safe to be complacent about serving your dog foods with onion in them. Here are the reasons why.

Things that make dogs more susceptible to onion poisoning

Some dogs are more susceptible to the effects of onion poisoning than others. Which means even a tiny amount of onion is more likely to hurt them. Canines which are more sensitive to onion poisoning include:

  • Small and miniature breeds
  • Puppies
  • Old dogs
  • Dogs with blood disorders, some autoimmune diseases, and some genetic mutations
  • Dogs with parasitic infections such as hookworm
  • And some specific breeds

For example there is evidence that Japanese dog breeds such as Akitas and Shiba Inus are more prone to onion-induced anemia.

Not all onions are created equal…

Furthermore, a harmful amount of onion doesn’t just depend on the dog. It can depend on the onion too. Onions grown in highly sulfurous soil, or places with high sulfur dioxide air pollution will have a greater concentration of sulfur compounds in them. Large areas of Louisiana and Texas have exceptionally large sulfur deposits of sulfur in their soil for example. And heavy traffic and burning coal or crude oil on an industrial scale both produce sulfur dioxide air pollution. So the same type and quantity of onion ingested on two separate occasions might not have the same effect on your dog both times. Don’t be assume that eating a small amount of onion won’t hurt them now, because it didn’t hurt them before.

In addition, bear in mind that cooked onion remains as toxic to dogs as raw onion, and that flavorings like onion powder are a concentrated form of onion.

Signs that your dog has eaten a toxic quantity of onion

Eating onion doesn’t usually make dogs sick straight away. Whilst the breakdown of red blood cells starts within 24 hours of eating onion, the damage peaks around 4 – 6 days later. In case studies reported to veterinary journals, dogs are usually taken to their veterinarian 2 or 3 days after eating onion. So, just because your dog isn’t showing any ill-effects 20 minutes or an hour after ingesting onion doesn’t mean that they haven’t been harmed by it. Symptoms to stay vigilant for are:

  • Faster, more shallow breathing
  • Vomiting
  • Dark red or brown urine
  • Diarrhea
  • Pale inner cheeks or gums
  • Seeming weak or depressed
  • Loss of appetite
  • Smell of onion on their breath
  • Increased heart rate

The normal resting heart rate for dogs varies and depends on things like their size. But if you’re used to cuddling up with your dog and you know the normal feeling of their pulse, you might recognize it getting more rapid.

Now let’s take a look at what you should do, if your dog eats onion – even a little bit.

Getting help – the Animal Poison Control helpline

The ASPCA’s Animal Poison Control Center is an invaluable resource for pet parents whose dogs have consumed small amounts of potentially toxic food, and aren’t showing any signs of poisoning yet. Their helpline is open 24 hours a day, 365 days a year. Their advisors will help you assess the risk to your dog, and whether they need immediate veterinary attention or just close monitoring at home for the time being.

When to go directly to a veterinarian

If your dog is showing any of the symptoms of onion poisoning, then arrange for them to see a vet immediately. Remember that sign of onion toxicity usually become apparent two or three days after eating onion, but the dog’s condition will continue to get worse for three or four days after that. Don’t wait for them to get even sicker!

The Labrador Handbook by Pippa Mattinson

Your veterinarian will be able to properly assess symptoms of onion poisoning that you can’t, such as the proportion of intact vs destroyed red blood cells in their bloodstream. With prompt treatment, onion poisoning is rarely fatal, and doesn’t cause any lasting harm. But the anemia may take several days to correct itself, and high blood pressure might last several weeks.

Will a small amount of onion hurt my dog

In a lot of cases, a small amount of onion won’t hurt a dog. As a rule, a quantity of onion equal to less than 0.5% of their body weight will not usually result in harm. But just a tablespoon or two of onion, or a few chips seasoned with onion powder, can be enough to hurt a puppy or a small adult dog. And the concentration of thiosulfinates – the anemia-triggering compounds in onions – is not uniform from one onion to the next. So, don’t be complacent about letting your dog eat small amounts of onion – keep it out of their diet whenever you can to be safe.

The Labrador Site Founder

Pippa Mattinson is the best selling author of The Happy Puppy Handbook, the Labrador Handbook, Choosing The Perfect Puppy, and Total Recall.

She is also the founder of the Gundog Trust and the Dogsnet Online Training Program 

Pippa’s online training courses were launched in 2019 and you can find the latest course dates on the Dogsnet website