Inert earth mineral used as a thickening, lubricating, and sunscreen ingredient in cosmetics. Along with titanium dioxide, zinc oxide is considered to have no risk of skin sensitization. It can also be a soothing agent and, potentially, an antioxidant. [1, 2] Nano-sized zinc oxide is not believed to be a safety concern for skin. 
- Ting W, Vest C, Sontheimer R. Practical and experimental consideration of sun protection in dermatology. Int J Dermatol. 2003;42(7):505-13.
- Burnett M, Wang S. Current sunscreen controversies: a critical review. Photodermatol Photoimmunol Photomed. 2011;27(2):58-67.