Vet Reviewed

By The Farmer's Dog | November 7, 2022

They seem innocuous enough–the crunch of acorns underfoot is one of those signs of autumn and harbingers of colder weather to come. But when it comes to your dog, acorns are actually quite dangerous.

“I don’t think many people know about acorn toxicity,” says Montauk, New York-based small animal veterinarian Molly Miosek. But in fact, crunching on acorns can cause mild to very severe stomach upset, intestinal obstruction, and in rarer cases, kidney or liver failure, and even death.

Why are acorns dangerous?

Acorns, the fruit of oak trees, are nuts, with the seed encased in a hard, leathery shell. They’re unsafe for dogs on a few different fronts. For one, they contain tannins, plant compounds that taste bitter and serve as antinutrients, which means they prevent the body from absorbing vitamins and minerals. 

If a dog eats small amounts consistently, say one acorn a day every day, over time the tannins can cause kidney and liver damage, Dr. Miosek says. Or, if a dog eats a larger number of acorns at once, they may take in enough tannins at once to get sick right away.

Acorns’ hard shells pose another danger, she adds. They can cause choking, or obstruction in the digestive tract. Plus, the jagged shells can tear small holes in the intestinal tract of a dog, causing damage and exposing them to bacteria.

You may have noticed that crunch underfoot is more pronounced some years than others—every 2 to 5 years, oak trees experience “masting,” a season in which they produce a much larger volume of acorns than usual. During these “mast events,” you’ll need to be even more vigilant about keeping acorns out of your dog’s mouth.

Incidentally, other parts of oak trees, such as the leaves, are also toxic to dogs. 

How do I know if my dog ate acorns?

Luckily, this is generally a one-season-per-year issue. Acorns generally begin falling in September and October. So, assuming it’s autumn, if your dog is lethargic, vomiting, has diarrhea (especially if it’s bloody), loses their appetite, or otherwise shows signs of stomach pain, they might have eaten acorns. (It’s likely that you’re not far from an oak tree; they grow in nearly every state in the U.S., and can live for up to 300 years. Make sure you’re aware of oak trees on your property and on your walking routes.)

One challenge is that there isn’t a magic number for how many acorns it takes to make a dog sick. It depends on the size of the dog–plus, acorns have varying amounts of tannins in them.

A perfect time to use the “leave it” skill is when you see your dog snuffling around acorns, so they learn they are not to be eaten. If you see your pup munch on one acorn, try to get them to drop it. If they don’t, and end up eating it, keep a close eye on them, and seek out care if they become ill, Dr. Miosek says. If you see your dog eat several acorns, take them to the vet right away. 

What’s the treatment?

Treatments may vary depending on your dog’s symptoms, but some to expect include IV fluids for hydration, and to flush out the tannins, and activated charcoal, as “that would coat and remove the material faster than anything else,” Dr. Miosek says. Your vet also may choose to give your dog a gastroprotectant, an antibiotic, anti-nausea medication, and/or a pain reliever. 

The best treatment, of course, is avoiding it in the first place. “I really want to stress prevention here,” she adds. “Watch your oak trees, watch your dog.”

This article was vetted by a vet.
Reviewed by Alex Schechter, DVM, founding veterinarian at Burrwood Veterinary.