What Should I Do if My Dog Ate a Small Piece of Onion?

Most dog owners know that chocolate is toxic. But if you gave your dog a meal with onion or you caught them using an onion as a chew toy, it might get you wondering—my dog ate a piece of onion; what should I do?

Onions are toxic to dogs, but the toxicity level depends on the dog’s size and how much they eat.

my dog ate a small piece of onion
What should I do if my dog ate a small piece of onion?

So, I’ll help you understand how to determine if your dog needs to see a vet after consuming onion and what toxicity symptoms to watch out for.

Determining if Your Dog Ate a Toxic Amount of Onion

Before you go into full-out panic mode, here’s the good news: Although onion is toxic to dogs, they can usually eat it in small amounts without harmful side effects.

The general rule of thumb is that it’s safe for dogs to consume up to 0.5% of their body weight in onions. 

Yes, I understand that it takes some calculating. So let me help you out.

If you own a six-pound Chihuahua, they can eat as much as 0.03 pounds of onion before they could experience life-threatening issues. In contrast, an 80-pound Labrador Retriever can consume as much as 0.4 pounds of onion with little chance of having harmful side effects.

The bottom line?

The amount of onion and your dog’s body weight combined makes the difference in whether they’ll have adverse side effects.

Pomeranian anxious looking
Pomeranian is anxious looking on the floor.

Why Onions Are Toxic to Dogs?

The reason that onions are toxic to dogs is that they contain n-propyl disulfide

I won’t get too scientific on you, but N-propyl disulfide breaks down red blood cells, which can result in anemia. Anemia is dangerous because it causes arrhythmia (irregular heartbeat) and an increased heart rate.

As a result, your dog’s heart has to work faster to pump blood throughout its body, leading to an enlarged heart, heart failure, and, in worst-case scenarios, death. 

Although some people can experience allergic reactions or issues with drug interactions when consuming onions, onions generally don’t have the toxic effect on humans as they do on dogs.

onion at the market
Is onion bad for dogs?

The Allium Species Conundrum

Onions are part of the allium species, which is a group of plants that can create toxic reactions to dogs. So, aside from eating onion, your dog could have an increased chance of toxicity if the onion-filled dish also contained allium species such as:

Luckily, most dogs won’t naturally want to gobble up these foods. That’s why toxicity from onion and other allium species more commonly occurs from them eating a dish containing one or more of these ingredients. 

If it’s any consolation, garlic is the most toxic of all the allium species; it’s about five times more toxic than onion.

garlic and chives
Garlic and chives are both toxic for dogs.

The Two Types of Onion Toxicity

As you’re contemplating, “My dog ate a piece of onion. What should I do?” there’s another layer to consider.

As if it couldn’t get worse for the worried dog owner, your dog may undergo one of two types of onion toxicity:

  1. Instant onion poisoning.
  2. Delayed onion poisoning.

Instant onion poisoning is the most common, as it occurs when your dog consumes significantly more than 0.5% of its body weight in onion.

You’ll notice symptoms of onion toxicity shortly after your dog eats onion if they’re going to have an “instant” reaction, although it could take as long as 72 hours.

The second type of onion toxicity is when N-propyl disulfide gradually builds up in your dog’s system by eating onions over several days. The toxin will then build up in their system, rearing its ugly head as it starts impacting your dog’s red blood cells.

Some dog owners may unknowingly be giving their dog a toxic amount of onions if they’re sharing leftover onion-containing food with their dog multiple days in a row.

For this reason, among many others, it’s best to stick with feeding your dog their canine-appropriate dog food.

Chihuahua feeling sick in the car
Chihuahua is not feeling well inside the car. Heading to the vet clinic!

Does It Matter if the Onion Is Cooked or Raw?

Dogs can react equally to onions, whether they’re cooked or raw.

Therefore, even though it’s gross (and seemingly unlikely unless they have pica), your dog can have onion toxicity by chowing down on raw onions and grabbing some fried onion rings off your kitchen counter. 

So, the rule of thumb is to always keep onions out of your dog’s reach regardless of what cooked state the onions may be in.

chocolate toy poodle eats food from a bowl
A chocolate Toy Poodle eating from a ceramic bowl

What About Powdered Onion?

Powdered onion is toxic for dogs, too, since it contains N-propyl disulfide. 

In fact, powered onion can be even more toxic since it’s so concentrated and easier for a dog to consume in greater amounts.

onion powder in white porcelain scoop
Onion powder is harmful to your dog’s health.

Watching for Signs of Onion Toxicity

If you feel your dog ate more than 0.5% of their body weight in onion, I encourage you to take them to the vet immediately. 

Otherwise, it’s still important to monitor your dog in the hours after they consume onion. Some signs that your dog is experiencing onion poisoning include:

  • Vomiting
  • Diarrhea
  • Lethargy
  • Collapse
  • Excessive panting
  • Irritation in the mouth
  • Stomach that’s sensitive to the touch

In more progressive cases of onion toxicity, your dog might develop pale gums, and their heart will start to race. At that point, taking your dog to the vet as quickly as possible is critical, as this is a dangerous and life-threatening state.

Dachshund lying on the floor
Dachshund lying on the clean floor.

How a Veterinarian Treats Onion Toxicity?

A veterinarian will take different approaches to treat onion toxicity depending on your dog’s symptoms and how much time has passed since they consumed the onion.

If you drove your dog to the vet as soon as you caught them eating onion, then your veterinarian will likely induce vomiting to help the onion get out of their system before the N-propyl disulfide has time to attack their red blood cells. 

Alternatively, they may use a tube to administer activated charcoal. Activated charcoal can be effective at removing toxins, as it’ll absorb them from your dog’s blood.

If your dog has a severe bout of onion toxicity, they’ll likely also put your dog on oxygen. That’s because, with a lack of red blood cells, your dog will experience reduced circulation, which is dangerous for their health.

In worst-case scenarios, your veterinarian might even perform a blood transfusion. Doing so will help stabilize your dog and allow its bone marrow to generate red blood cells, which will allow them to leave the vet with a new lease on life.

You can also expect your veterinarian to run blood tests, checking for your dog’s red blood cell status and oxygen levels.

Pug in a vet clinic
Pug getting a check-up in a veterinary clinic.

How To Prevent Your Dog From Eating Onions?

Although most dogs won’t want to eat onions raw, they could see raw onions as a play toy. And, of course, it can be hard to hide the scent of cooked onions, especially if you’re giving them cooked onions with meat.

So, some of the best ways to prevent your dog from eating onions include:

  • Keep raw onions out of reach of your dog.
  • Never feed them foods with onion or onion powder.
  • Don’t leave onion-filled food on the counter.

Of course, if your dog is grabbing food off your counter, you have an entirely separate issue on your hands. There’s nothing that some good, consistent training can’t take care of, though.

If you want to feed your dog raw onions for whatever reason, you can give them several safe fruits and vegetables instead. Carrots, apples, celery, bananas, beets, and cucumber are some of the many dog-friendly foods.

Contrary to popular belief, dogs are omnivores. That’s why dog food often contains vegetable ingredients. So, you’re welcome to add veggies to your dog’s diet as long as they’re not in the form of onions and certain other toxic plants.

samoyed-dogs-getting-hungry
Samoyed dogs in the kitchen, waiting for their food.

The Bottom Line

It isn’t always common knowledge that onions are toxic to dogs. So if you came here searching “My dog ate a piece of onion,” I applaud you for being proactive in figuring out what to do.

Not all dogs that eat onions need to go to the vet. If they consume 0.5% of their body weight or less in onions, their bodies will likely be able to manage the onion without treatment.

Nevertheless, I know it can be hard to determine the weight of how much onion your dog ate. Plus, like any good dog owner, you’re understandably worried about your pooch. So, when in doubt, it’s always wise to take your dog to the vet for peace of mind.