Xylitol is a sugar substitute that is found in everything from chewing gum to peanut butter to ice cream to toothpaste. It’s often listed under other names, including birch sugar, birch extract, or wood sugar. While considered safe for humans, xylitol is highly poisonous to dogs. If a dog consumes xylitol, blood sugar can drop dangerously low, resulting in seizures, liver failure, and even death.