Nanocosmetics: The Good, the Bad and the Beautiful

Abstract

Nanotechnology has found extensive applications in the field of cosmetics. Nanoscale materials have the potential to enhance the effectiveness and affect the cellular responses as- sociated with various cosmetics. Depending on the type of nanoparticle used, the effects seen may vary. The common applications of nanoparticles in cosmetics are to enhance their physi- cochemical properties and the visual appeal of the cosmetic, enhance stability of the actives, modulate penetration of actives, alter the route of penetration (intercellular, transcellular or ap- pendageal), cause site specific accumulation, modulate systemic toxicity of actives or enhance the intrinsic photostability of the cosmetics.1 The size of nanocarriers influences their dermal penetration and cellular internaliza- tion. This may be utilized for beneficial purposes such as a size dependant accumulation of the nanocarriers may be obtained in various layers of the skin. The effects are specific to each type of nanoparticles and hence there is no common cellular effect of all nanoparticles. Many factors determine the ultimate effect of the nanoparticles in cosmetology. While size is a major determinant of the effects of nanoparticles in the skin, another important parameter influencing the effects of nanoparticles in cosmetics is their soluble, in- soluble, degradable or non-degradable nature. This distinction is evident in the European Union cosmetic regulation which defines nanomaterials as “insoluble or biopersistant and intention- ally manufactured materials with one or more external dimensions or an internal structure on a scale of 1 to 100 nm.”2 Cellular responses, residence time and depth of penetration through intact skin can widely vary depending on this property of nanomaterials. Quantum dots are a group of non-degradable nanoparticles that have been explored in several applications for their optical properties. In general, quantum dots have not been found to penetrate through the stratum corneum; however, there is evidence that some accumulation in the epidermis is possible with changes in pH, surface chemistry of the shell of the quantum dot.3 Nevertheless, more clarity is required on the biological effects of this group of nanopar- ticles. Titanium dioxide and zinc oxide nanoparticles have been widely used in sunscreens.4 Zinc oxide nanoparticles have often been found to be localized on the surface of the skin and hair follicle shafts without deeper penetration. Recently, zinc oxide nanoparticles have