Onions are a common ingredient in so many everyday meals that it is worth being very clear on this one. Can dogs eat onions? No, they cannot. Onions are toxic to dogs and can cause a type of anaemia that damages red blood cells, making it harder for the body to carry oxygen around. All parts of the onion are harmful, whether raw, cooked, powdered, or dehydrated, and the same applies to the wider allium family, which includes garlic, leeks, chives, and shallots.
Onion toxicity in dogs is caused by compounds called thiosulphates, which dogs cannot metabolise in the way humans can. These compounds attack red blood cells and cause what is known as haemolytic anaemia. The effects are not always immediate, which can give a false sense of reassurance. Symptoms may take several days to appear, by which point significant damage may already have occurred. Dogs with heart conditions or those that are already anaemic are at greater risk of serious complications.
How Much Onion Is Dangerous?
Onion toxicity is generally considered to occur at around 0.5 percent of a dog’s body weight, meaning a 20kg dog could potentially be harmed by eating just 100g of onion. However, repeated smaller exposures over time can also cause cumulative damage, which means the occasional scrap of food containing onion is not as harmless as it might seem. Onion powder is particularly concentrated and can be harmful in even very small quantities.
This is worth keeping in mind when it comes to sharing leftovers or table scraps. Gravies, stocks, soups, stews, sauces, and many ready-prepared foods frequently contain onion or onion powder, often in quantities that are not obvious from the outside. Dogs with existing health conditions can be more vulnerable, but the risk applies to all dogs.
Symptoms of Onion Toxicity in Dogs
Signs of onion poisoning can include lethargy, weakness, reduced appetite, pale or yellowish gums, rapid breathing, and collapse in severe cases. Vomiting and diarrhoea may also occur. Because symptoms can be delayed by several days, it is important to contact your vet as soon as you know your dog has eaten onion, rather than waiting to see how they seem. Early treatment is always more effective.
Your vet may recommend inducing vomiting if the ingestion was very recent, followed by monitoring and supportive care. In serious cases, a blood transfusion may be required. Dogs with pre-existing conditions may need closer monitoring and more intensive treatment.
Hidden Sources of Onion
Onions are present in a surprisingly wide range of foods that might not be immediately obvious. Baby food sometimes contains onion powder. Many packet sauces, seasonings, and stock cubes include it. Leftover pasta sauces, casseroles, and roasted meats cooked with onion all carry a risk. If you are in the habit of giving your dog scraps from the table or cooking pot, it is worth being very mindful of what went into the dish. Garlic bread, as previously noted in our guide on can dogs eat bread, is another common offender.
It is also worth checking any commercial dog treats or foods if your dog has had an unexplained reaction, as some lower-quality products have in the past contained trace amounts of onion or garlic. Reading labels is a habit worth getting into. For a broader picture of food safety, our guides on can dogs eat grapes and can dogs eat chocolate cover two of the other most important foods to keep away from dogs.
What to Do If Your Dog Eats Onion
Contact your vet straight away, even if your dog seems fine. Let them know approximately how much your dog ate and in what form, whether raw, cooked, or powdered. Do not wait for symptoms to develop. Having dog insurance means that the cost of emergency treatment is not a barrier to getting your dog the help they need as quickly as possible. You can compare cover options at Quote & Save.
The Short Answer
Can dogs eat onions? No, under no circumstances. Onions are toxic to dogs in all forms and can cause serious, potentially life-threatening anaemia. Keep onions and all allium family vegetables well away from your dog, and be vigilant about the hidden sources in everyday cooked food.
