Is it an allergic reaction if your tongue gets numb from gum?

No. Your tongue going numb from gum is a common temporary side effect of a dental anesthetic used during dental procedures to help numb the site being worked on. This sensation is usually temporary and harmless, and should go away within a few hours. On the other hand, an allergic reaction to something such as an ingredient in the gum would likely cause hives, difficulty breathing, or other more severe symptoms.