Can Cats Eat Onions?

Are onions and their relatives safe for cats to eat? In a word, the answer is NO. Onions are part of the Allium species of plants along with garlic. While many types of onions are root vegetables with the actual onion growing below ground, some onions, like scallions, grow their edible portions both below and above ground. Onions include white, yellow, and red onions, leeks, chives, and scallions.

The ingestion of onions initiates chemical processes within the cat's body that act upon their red blood cells (erythrocytes). The interaction of these substances destroys those blood cells so they can't do their job of transporting oxygen to the cat's tissues. The result is hemolytic anemia, and the formation of a clot-like abnormality called a Heinz body which can add to the destruction and dysfunction. Symptoms resulting from de-oxygenation can occur in all organs and tissues. One of them, dehydration can cause severe illness and even death if it's not treated properly.

Cats don't typically eat raw onion outdoors, and ingesting cooked onion in human food is the most common way our cats can develop onion poisoning. Upon cooking, onions lose some of their sharp taste and become sweet. Rubbing their fur on an onion plant or the onion itself may also cause toxicity as the cat cleans itself.

Even tiny amounts of onion can cause onion toxicity in a vulnerable purr baby, but the rule of thumb is that a 10-pound cat will become ill by eating about one and a half tablespoons of the toxic food (25 grams), or about 0.5% of their body weight. Japanese breeds are commonly more susceptible to hemolytic changes after ingesting onion, its juice, or its leaves and stem. Kittens and older cats may also experience symptoms after ingesting only a tiny amount.

If a cat eats a large amount of onion at one time, or over a period of a few days, they can experience severe symptoms, including abdominal pain, blood in their urine and stools, and exercise intolerance. Eventually, there may be liver and kidney damage. A smaller amount may cause milder, more short-lived symptoms.

Medications such as acetaminophen, certain antibiotics, and some human supplements can make a cat vulnerable to the effects of onions in their body that may cause methemoglobinemia which stops oxygen from getting to the body's tissues. 

Other forms of onion, like dried onion flakes or onion powder, can cause toxicity as well. For this reason, it's a good idea to store these flavor enhancers where a cat can't access them. Baby food often contains onion flavoring in the form of juice or powder, so it's important not to give it to your feline, and to remove used containers and utensils promptly. Leftover human food like pizza is also tasty but dangerous to a cat, as it may contain onion powder or fresh onion in its sauce or even as a topping. It's a good idea to assume that any human food might contain a form of onion and to feed a cat only food and treats meant for them.

A cat will begin to exhibit signs of poisoning within a few hours of eating an onion (though in some cases it may take longer). These symptoms may include:

• Depression
• Blood in the urine or stools
• Yellowing of the white part of the eyes or skin (jaundice)
• Rapid breathing
• Rapid heartbeat
• Weakness
• Inability to move around
• Sensitivity to cold
• Reduced appetite
• Abdominal pain
• Diarrhea
• Onion breath

If you suspect that your cat has ingested any form of onion, especially foods containing concentrated onion powder or juice, a visit to your vet or emergency clinic is important to assess the toxicity level and treat the effects. The Pet Poison Hotline can also help to identify onion poisoning and may have suggestions for what you can do at home if the condition is mild. 

It's not recommended that cat parents attempt to induce vomiting. If this treatment is necessary, the veterinarian will do it, along with tests to confirm the diagnosis and treatments to minimize damage to the cat's organs. 

Raw onions' pungent aroma and sharp taste will most likely repel a cat. However, if the onion is cooked, it becomes more palatable and your purr baby may eat whatever tasty food it's in. Sauces, gravies, and soups are especially attractive to a feline.

With treatment such as fluid therapy and diluted N-acetylcysteine, symptoms of onion poisoning will typically subside over a few days, depending on the severity. Full recovery requires that the cat's bone marrow replaces damaged red blood cells with healthy ones. Full erythrocyte regeneration takes approximately 10 to 12 days if the kitty has no complicating factors such as pre-existing conditions, is a kitten or senior, or is a susceptible breed.  

In addition to Japanese breeds being more vulnerable to serious poisoning, there are some conditions often associated with severe onion toxicity, such as diabetes, fatty liver, hyperthyroidism, and certain types of cancer like lymphomas.

Restricting access to onions, especially those cooked into foods is key to preventing onion toxicity in cats. Given sufficient treatment and support, many of these pets will recover, but the condition can also cause death if it's severe enough or goes untreated. Awareness of the signs of onion poisoning is a cat parent's best defense against this serious disorder.

A high-quality diet free of onions in any form is essential for keeping your cat happy and healthy. Onion toxicity can be expensive to treat. Compare pet health insurance plans to save more than $270 a year on vet care.