Chewing Gum is Toxic Is Chewing Gum really the Most Toxic Substance in the Supermarket? The number 1 Ingredient : Gum Base. ⁠⁠Imagine if someone said, “Hey, would you like to chew on some tire rubber or plastic?” You probably would politely decline. (maybe laugh) But this isn't far off what gum is; “Gum base” is a blend of elastomers, plasticizers, fillers, and resins. Other ingredients are polyvinyl acetate, which is frequently referred to as “carpenter glue”. Paraffin wax is another ingredient that is a byproduct of refined petroleum.