Cosmetic products with gold nanoparticles display enhanced anti-aging, moisturizing, and regenerative effects, which are mostly based on their sizes, shapes, surface charges, and dose of application. The use of nanoparticles as cosmetic additives raises questions about their safety, for which information is often obtained by testing them independently of the cosmetic product. As their physicochemical qualities depend on the surrounding medium, a more appropriate approach is to characterise them in the complex medium of the cosmetic product. For this reason, we have studied the physicochemical properties of gold nanoparticles in a commercial skin care cream, for observing possible changes in their sizes, shapes and surface, as the surrounding medium is a critical factor for these properties which subsequently determine their beneficial or harmful effects in cosmetic products.
