Nanomaterials are being used in cosmetic products for various effects. However, their use also raises potential safety concerns. Some of these concerns can be addressed by determining the type of nanomaterials used, as well as stability, potential for skin absorption, route of exposure, and how they are formulated in cosmetic products. There has been considerable effort internationally to harmonize approaches in order to address definitional issues and safety concerns related to the use of nanomaterials in cosmetic products.