All members of the allium family are toxic to dogs — onions, garlic, leeks, chives, shallots, spring onions and their powdered forms. They contain organosulphur compounds that damage dogs' red blood cells, causing haemolytic anaemia. Cooking does not neutralise the toxin; dried powders are actually more concentrated. This guide covers why alliums are dangerous, what dose matters, and the surprising number of human foods that contain them.
Alliums are one of the most important toxins for UK dog owners to understand — not because they cause sudden death (they rarely do), but because they are hidden in almost every savoury human dish. Gravy, soup, stock, sauces, stir-fries, baby food, ready meals, crisps, pre-made coleslaw and salad dressings all commonly contain onion or garlic powder. A dog being "given a taste" of Sunday dinner is, in many cases, being given a low but repeated dose of allium toxin.
Which Alliums Are Toxic?
All of them. The whole family contains the same organosulphur compounds — the only variables are concentration and palatability.
| Allium | Relative potency | |---|---| | Garlic | Most potent — ~5x more than onion | | Wild garlic (ramsons) | Same as cultivated garlic | | Onions (all colours) | Baseline toxicity | | Shallots | Between onion and garlic | | Leeks | Same toxin, lower concentration | | Spring onions | Same toxin | | Chives | Lowest concentration of the family | | Onion powder | More concentrated than fresh onion | | Garlic powder | More concentrated than fresh garlic | | Dehydrated onion flakes | Very concentrated |
Why Alliums Are Toxic to Dogs (But Not Humans)
Alliums contain compounds called n-propyl disulphide and thiosulphates. In dogs (and cats), these compounds attach to haemoglobin in red blood cells and cause oxidative damage. The damaged cells form "Heinz bodies" and are then destroyed by the spleen, leading to anaemia.
Humans have different red blood cell biochemistry — we can process these compounds without harm. Dogs cannot. The toxicity is cumulative over several days, which means repeated small doses can be as dangerous as one large dose.
How Much Is Toxic?
The commonly cited threshold is 15-30g of onion per kg of body weight, or about 5g of garlic per kg — but repeated lower doses cause the same anaemia. A 5kg dog eating a clove of garlic daily for four days is at real risk. There is no fully safe dose, and sensitivity varies by breed: Japanese breeds (Akitas, Shiba Inus) are especially susceptible.
Practical translation:
- A single small leaf of chives on a baked potato is very unlikely to cause symptoms in a large dog.
- A whole raw or cooked onion for any dog is an emergency.
- One teaspoon of garlic powder is dangerous even for a large dog.
- A bowl of stew flavoured with onion and garlic powder is dangerous for a small dog even if it doesn't contain visible pieces.
The Hidden-Allium Problem
This is where most real-world allium poisoning happens. The following are very commonly seasoned with onion or garlic powder:
- Gravy, soup, stock cubes and broths
- Shepherd's pie, spaghetti bolognese, risotto, lasagne, stir-fries — the savoury base of almost every cooked dish
- Sausages and sausage rolls, burger mince, meatballs, kebabs
- Salsa, dips and chutneys
- Pizza, garlic bread, stuffing, pesto
- Crisps and savoury snacks (onion-flavoured crisps, cheese-and-onion anything)
- Baby food — many savoury baby foods contain onion
- Salad dressings, mayonnaise variants, ready-made coleslaw
- Tinned soups and stews, ready meals, pie fillings
- Sandwiches — particularly coronation chicken, tuna mayo, egg mayo
- Takeaways — Indian, Chinese, Thai, Italian, Mexican are all allium-heavy
If you don't cook it yourself with no allium seasoning, assume it contains onion or garlic.
Symptoms and Time Course
Hours 0-12 (gastrointestinal phase):
- Vomiting, diarrhoea, loss of appetite, drooling, abdominal pain
- Excessive thirst
Hours 24-72 (haemolytic phase):
- Pale or yellowish gums
- Lethargy, weakness, reluctance to walk
- Rapid breathing, rapid heart rate
- Red-brown or dark urine (haemoglobinuria) — a classic sign
- Collapse in severe cases
Days 3-7 (anaemia phase):
- Ongoing weakness
- Persistent pale gums
- In severe cases, jaundice
Because the haemolysis is delayed, a dog that seems fine 6 hours after eating onion is not out of the woods. Blood tests at 2-3 days post-ingestion are often needed.
What to Do If Your Dog Eats Alliums
- Note what was eaten. Raw onion, cooked onion, onion powder, a dish containing onion? Weigh or estimate the quantity.
- Note your dog's weight.
- Call your vet or the Animal PoisonLine (01202 509000). They will calculate the dose and advise based on severity.
- Do not induce vomiting unless told to. If your vet decides to decontaminate (activated charcoal, fluids), this is a veterinary procedure.
- Monitor for 7 days. Look for the symptoms above. Even a dog that seems fine at 24 hours can develop anaemia at day 3-5.
Review signs of poisoning in dogs, when to call the vet, and the broader foods toxic to dogs list.
Prevention
- Read labels. Any savoury ready meal or sauce you share with your dog — read the ingredient list for onion, garlic, shallot, or leek.
- Don't "give a taste" of seasoned food. Even a spoonful of Bolognese is problematic for a small dog.
- Keep allium vegetables and powders out of reach. Onions left on a chopping board, garlic bulbs in a fruit bowl, and spice jars on a low shelf are all common sources of accidental ingestion.
- Cook plain for your dog. Plain cooked chicken, rice, or sweet potato with no seasoning is the reliable format.
- Train food-stealing behaviour out. Counter-surfing and bin-raiding dogs are the most common allium poisoning cases.
Bottom Line
Alliums are everywhere in human food. Dogs cannot process them safely. Cooking makes them more concentrated, not less. If you remember only one thing: the savoury base of human cooking — the onion, the garlic, the stock — is not for your dog. When in doubt, cook separate and keep it plain.