Glucose oxidase is an enzyme that oxidizes glucose into gluconic acid, which converts oxygen into hydrogen peroxide in the process. This enzyme is naturally found in honey, and it is the reason why honey can sit in your kitchen cupboard for months (or even years) without going bad. In cosmetics and personal care products, glucose oxidase functions as a natural preservative. It is able to kill bacteria because it releases hydrogen peroxide when converting glucose to gluconic acid. Hydrogen peroxide is toxic to bacteria. Glucose oxidase is typically used in combination with lactose peroxidase for full preservative effect in a cosmetic formulation.