Is Xylitol really dangerous to dogs? Xylitol is toxic to dogs and even small amounts can cause seizures and death. Just a few years ago, Xylitol wasn’t a big problem to dog owners. The substance mostly appeared in chewing gums, and there’s no reason to give a dog a chewing gum. Nowadays, the sweetener is common in everything from sugar free cookies to peanut butter – foods much more likely to be eaten by a dog. Symptoms appear between 30 minutes to 12 hours after the dog ate Xylitol. Minutes count – if you suspect your dog ingested Xylitol, contact your veterinarian or pet ER immediately.