Can Dogs Eat Onions?

Why onions are toxic to dogs

Onions contain sulphur compounds, including N-propyl disulphide and other thiosulphates. In dogs, these compounds cause oxidative damage to red blood cells, the cells that carry oxygen around the body.

The damaged cells form small clumps of altered haemoglobin called Heinz bodies. The body sees these cells as faulty and destroys them faster than it can replace them. The result is a type of anaemia called Heinz body anaemia. In severe cases, a dog may not have enough red blood cells to carry the oxygen it needs.

Humans don't react to onions in the same way, which is why a food that is safe on your plate can be dangerous in your dog's bowl.

Every form is dangerous

Cooking, drying and powdering do not make onions safe. That includes:

• Raw onion, red, white or yellow
• Cooked, fried or caramelised onion
• Dried onion flakes
• Onion powder and onion salt, which are concentrated and easy to miss
• Spring onions (scallions)

The onion family

Onions belong to the Allium family. Its other members cause the same problem:

How much onion is dangerous?

A commonly quoted veterinary figure is that eating onion equal to about 0.5% of a dog's body weight can be toxic. Here's what that looks like:

For comparison, a medium onion often weighs somewhere around 100 to 150 g. So a small dog can reach a toxic dose from a fraction of one onion.

Treat these numbers as a rough guide, not a safe limit. Dogs vary in how sensitive they are. Small amounts eaten over several days can also add up, for example from leftovers or table scraps. Onion powder and garlic are more concentrated, so less is needed.

Are some dogs more at risk?

Any dog can be affected, but some are more vulnerable:

• Small dogs, because they reach a toxic dose with much less onion.
• Dogs that eat onion regularly, for example from shared dinners, because the damage can build up over time.
• Dogs that are already anaemic or unwell, because they have fewer healthy red blood cells to spare.
• Some Japanese breeds, such as Akitas and Shiba Inus. Veterinary references note that their red blood cells may be more sensitive to this kind of damage.

Cats are even more sensitive to onions than dogs, so keep onion and garlic away from every pet in the house.

Symptoms of onion poisoning

The signs come in two stages.

Within about a day:

• Vomiting
• Diarrhoea
• Drooling
• Belly pain
• Loss of appetite

Often several days later, as red blood cells are destroyed:

• Pale gums
• Weakness, tiredness and not wanting to walk
• Fast breathing or panting at rest
• A fast heartbeat
• Red or brown urine
• Yellow gums or eyes, in some cases
• Collapse, in severe cases

Because the anaemia is delayed, a dog can seem completely fine for a few days before it becomes unwell.

My dog ate onion. What should I do?

1. Call your vet or an emergency vet. In the US you can also call the ASPCA Animal Poison Control Center at (888) 426-4435 (a fee may apply). In the UK, your vet can contact the Veterinary Poisons Information Service.
2. Don't make your dog vomit at home unless a vet tells you to.
3. Have the details ready: what your dog ate, roughly how much, when, and your dog's weight. Keep the packaging or recipe if you can.
4. Watch your dog closely over the next few days, and check the colour of its gums and urine.

If your dog ate onion recently, the vet may make it vomit and give activated charcoal. They may run blood tests to check red blood cell levels over the following days. Dogs with severe anaemia may need oxygen, fluids or a blood transfusion. Most dogs recover when the problem is caught and treated.

Where onions hide

Whole onions are easy to spot. These are the sources owners miss:

• Gravy and stock cubes: many contain onion or garlic powder
• Baby food: some savoury jars contain onion powder, so check the label before using it to tempt a sick dog
• Pizza: onion in the sauce, toppings and garlic in the crust
• Takeaway food: curries, stir fries, kebabs and burgers are often full of onion and garlic
• Soups, stews and sauces: onion is a base ingredient in most of them
• Seasoning mixes and crisps: onion powder is common
• Stuffing and roast dinners: a classic holiday risk

Safe foods to share instead

Plain cooked chicken with no seasoning, a slice of apple without the core, or a piece of banana are all safer choices. Not sure about another food? Check it in the Dog Food Checker.

FAQ

Are cooked onions safe for dogs?

No. Cooking does not destroy the compounds that harm red blood cells. Raw, cooked, fried, dried and powdered onion are all dangerous.

My dog ate a small piece of onion. Will it be OK?

A small piece is unlikely to cause serious harm in a large dog, but the risk depends on your dog's size, the amount and whether it has eaten onion before. Call your vet for advice.

Is garlic worse than onion for dogs?

Garlic is generally considered more potent than onion, so a smaller amount can cause harm. Keep both away from your dog.

How long after eating onion will my dog show symptoms?

Stomach upset can start within a day, but signs of anaemia often take several days to appear. A dog can seem fine at first.

Can dogs eat food cooked with onion if I pick the onion out?

It's best not to. The compounds can soak into gravy, sauces and meat juices, so removing the visible pieces doesn't remove the risk.

Sources

• Merck Veterinary Manual
• ASPCA Animal Poison Control Center
• PDSA

This article is general information, not a replacement for advice from your vet.