Xylitol is an artificial sweetener that's commonly found in sugar-free gum and other low-calorie foods. Because it tastes sweet but doesn't actually contain calorie-laden sugar, it's a great way to indulge your sweet tooth without adding to your waistline. But it's this very function that makes it so dangerous for dogs: when a dog's pancreas sees xylitol in the system, it mistakes it for real sugar and unleashes a flood of insulin. That insulin causes a dangerous drop in the dog's blood-sugar levels, leading to a series of life-threatening symptoms including vomiting, weakness, staggering, lack of coordination, collapse, and seizures.
You're probably not planning to feed Fido gum anytime soon. But for avid chewers who keep packs on their desk, in their cabinets, on their nightstand, take note: Xylitol, a sweetener in sugar-free gum, is seriously dangerous to dogs.