Zinc oxide works so incredibly well as a sunscreen because it is a physical barrier between your skin and the sun. Its sits on top of your skin and prevents the suns UV rays from dmaaging your skin. Using non nano Zinc Oxide which means its has larger molecules makes sure that the Zinc oxide does not absorb into the skin. Most sunscreens that use nano particles ingredietns are very toxic to the body and disrupt the endocrine system. Your endocrine is your hormonal system.