Gum can be fatal to dogs when eaten. Many gum brands contain xylitol, an artificial sweetener that is toxic to dogs. Xylitol causes a dog's blood-sugar level to drop to critical levels.
When xylitol enters a dog's system, it provokes a sudden and massive production of insulin. This lowers the glucose level in the dog's blood and can cause seizures and liver failure. These symptoms present themselves 30 minutes to 12 hours after the xylitol is ingested. A dose of 50 milligrams per pound of a dog's body weight is sufficient to cause the adverse reaction. According to VCA Animal Hospitals, xylitol is 100 times more toxic to dogs than chocolate. Xylitol is a common ingredient in both sugarless and regular chewing gum.