- Not a substitute for professional veterinary help.
Onions are a staple in many kitchens and an ingredient in many packaged foods, like ready-made meals, sauces, canned goods, and seasonings. They’re also very dangerous for dogs and cats, so it’s important to keep all foods containing onion away from your pets.
Dogs shouldn’t eat any amount of onions, but the risk depends on your pet’s size and how much onion they eat, says Dr. Wonjae Lee, medical director at Blue Cross Pet Hospital.
“Larger dogs need to eat more to get sick, but small dogs and cats can be harmed by even a tiny amount of onion,” Dr. Lee says.
Because every dog is different, it’s always safest to call your vet if you know or suspect your dog has eaten onion. Even small amounts can cause serious problems, and symptoms don’t always appear right away.
Read on to learn early signs of onion poisoning in dogs and what to do in an emergency.
How Much Onion Is Toxic?
“All forms of onion are unsafe—raw, cooked, dried, or powdered. Cooking does not make onions less toxic. In fact, cooked onions are more concentrated because they shrink, so a small amount can be just as dangerous,” Dr. Lee says.
Onions and other alliums like garlic, leek, and chives contain natural chemicals that can damage a pet’s red blood cells. Red blood cells carry oxygen around the body, and damage to these cells can cause anemia and weakness, and in severe cases, death.
“Any amount of onion ingestion can cause damage to red blood cells, but illness doesn’t occur until more red blood cells are destroyed than the body can regenerate,” says Dr. Kattlynn Cooper, veterinarian at Lyon Veterinary Clinic.
“As a general rule, eating more than about 0.5% of body weight in onion at one time can be dangerous,” Dr. Lee says.
Don’t forget about hidden onions, too. Dr. Cooper says onion powder is much more potent than fresh onions. You’ll find onion powder in many seasonings and sauces. Always check the ingredient labels before you let your pup have a lick of your plate!
Early Signs of Onion Poisoning
Signs of onion poisoning often don’t appear right away, Dr. Lee says, which can make it tricky to recognize.
In some pets, the first symptoms of onion poisoning may be mild and may show up within a few hours of eating onion.
Dr. Cooper says early signs can include:
- Vomiting
- Diarrhea
- Abdominal pain
- Loss of appetite
- Depression
- Evidence of dehydration
These early signs might seem minor, but onion poisoning has a delayed effect. This means your dog can suddenly become very sick days later as the condition progresses.
Emergency Signs of Onion Poisoning
“While early signs can sometimes pass unnoticed, the more dangerous effects usually appear later, often two to five days after ingestion, once the damage to the red blood cells has had time to develop into anemia,” Dr. Lee explains.
Dr. Lee says it’s a medical emergency if your dog shows any of the following signs:
- Pale gums
- Weakness
- Collapse
- Rapid or labored breathing as the body struggles to get enough oxygen
- Dark or reddish urine, which is caused by the breakdown of red blood cells
This combination of delayed onset and gradual worsening is what makes onion poisoning particularly dangerous, since a pet may seem fine at first but then suddenly become very sick several days later.
For this reason, contact your vet as soon as you notice—or even suspect—your dog has eaten onions. Let your vet know even if your dog seems fine at first. Acting quickly allows treatment to begin early and helps prevent serious illness.
How To Monitor Your Dog if They’ve Eaten Onions
If you think your dog may have eaten onions, staying calm and acting quickly can make a big difference. Here’s what to do:
- Figure out what they ate and how much: Note whether your dog ate raw, cooked, or powdered onion, along with the estimated amount they ate. Your vet will need this info to decide on next steps.
- Call your vet clinic for advice: Even a small taste can be risky, depending on your dog’s size. The clinic can tell you whether to monitor your pup at home or bring them in for treatment.
- Pay attention for symptoms: Watch your dog closely for any vomiting, diarrhea, fatigue or lethargy, pale gums, or changes in breathing. These signs may appear anytime within a few hours to a few days. Signs of hemotoxicosis, or blood poisoning, develop anywhere from a day to a week after eating onions, Dr. Cooper says.
- Offer plenty of water: Keeping your dog hydrated helps support their system while they process any harmful compounds.
If you can’t reach your veterinarian right away, you can call a pet poison hotline for guidance:
- ASPCA Animal Poison Control Center: (888) 426-4435
- Pet Poison Helpline: (855) 764-7661
What To Expect at the Vet Clinic
Your vet can do a few different things to help a dog who’s eaten onion, Dr. Lee explains.
If the ingestion occurred within the past couple of hours, your vet may induce vomiting or administer activated charcoal to help keep your dog’s body from absorbing the toxin.
Other treatments include:
- Fluids
- Anti-nausea medication
- Blood tests to monitor anemia
- Blood transfusions (for severe cases)
“With quick treatment, many pets recover well. The outcome is more serious if the anemia becomes very severe or if other organs, like the kidneys, are affected, but that is less common,” Dr. Lee adds.
The most important step is prevention! Take care to keep onions and any foods that contain them out of your pet’s reach, and always check ingredient labels before sharing any food with your pets. Soups, sauces, gravies, and even baby foods may contain onion and garlic powder.
