I wonder if it's the Sucralose, a chemical completely unrelated to sucrose(table sugar) and was originally developed as a pesticide. I used Listerine for many years before I developed a severe allergy to Sucralose. It started with the skin inside my mouth peeling slightly, it wasn't painful at all just kind of weird. Eventually I began getting hives and rashes on my hands and arms and slowly it kept getting worse and worse. If I use mouthwash or use toothpaste with Sucralose today I'll have very bad hives all-over hives that'll persist for a couple days. Ingesting any via food/snacks means a week of hives and needs a round of predisone to feel somewhat normal until it's all gone from my system.